diff --git a/src/MaterialDesignThemes.Wpf/Clock.cs b/src/MaterialDesignThemes.Wpf/Clock.cs
index ce0cf2ca3f..f4f0f5d683 100644
--- a/src/MaterialDesignThemes.Wpf/Clock.cs
+++ b/src/MaterialDesignThemes.Wpf/Clock.cs
@@ -58,12 +58,44 @@ public Clock()
     }
 
     public static readonly DependencyProperty TimeProperty = DependencyProperty.Register(
-        nameof(Time), typeof(DateTime), typeof(Clock), new FrameworkPropertyMetadata(default(DateTime), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, TimePropertyChangedCallback));
+        nameof(Time), typeof(DateTime), typeof(Clock), new FrameworkPropertyMetadata(default(DateTime), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, TimePropertyChangedCallback, CoerceTime));
+
+    /// <summary>Optional synchronous rule for minute slots, used for all selection paths.
+    /// Receives a date and time with seconds cleared. Keep the rule fast and free of side effects.</summary>
+    public static readonly DependencyProperty IsTimeAllowedProperty = DependencyProperty.Register(
+        nameof(IsTimeAllowed), typeof(Predicate<DateTime>), typeof(Clock), new PropertyMetadata(null, SelectionRulesChanged));
+
+    public Predicate<DateTime>? IsTimeAllowed
+    {
+        get => (Predicate<DateTime>?)GetValue(IsTimeAllowedProperty);
+        set => SetValue(IsTimeAllowedProperty, value);
+    }
+
+    /// <summary>Refresh after data captured by IsTimeAllowed changes. Call on the UI thread.</summary>
+    public void RefreshTimeAvailability()
+    {
+        CoerceValue(TimeProperty);
+        UpdateButtonAvailability();
+    }
+
+    private static object CoerceTime(DependencyObject d, object value)
+    {
+        var clock = (Clock)d;
+        return TimeSelectionRules.Nearest((DateTime)value, clock.IsTimeAllowed) ?? clock.Time;
+    }
+
+    private static void SelectionRulesChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+    {
+        var clock = (Clock)d;
+        clock.CoerceValue(TimeProperty);
+        clock.UpdateButtonAvailability();
+    }
 
     private static void TimePropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
     {
         var clock = (Clock)dependencyObject;
         SetFlags(clock);
+        clock.UpdateButtonAvailability();
         TimeChangedEventArgs args = new(TimeChangedEvent, (DateTime)e.OldValue, (DateTime)e.NewValue);
         clock.OnTimeChanged(args);
     }
@@ -126,6 +158,9 @@ private static void IsPostMeridiemPropertyChangedCallback(DependencyObject depen
             clock.Time = new DateTime(clock.Time.Year, clock.Time.Month, clock.Time.Day, clock.Time.Hour + 12, clock.Time.Minute, clock.Time.Second);
         else if (!clock.IsPostMeridiem && clock.Time.Hour >= 12)
             clock.Time = new DateTime(clock.Time.Year, clock.Time.Month, clock.Time.Day, clock.Time.Hour - 12, clock.Time.Minute, clock.Time.Second);
+
+        SetFlags(clock);
+        clock.UpdateButtonAvailability();
     }
 
     public bool IsPostMeridiem
@@ -419,6 +454,7 @@ private void GenerateButtons(
             button.SetBinding(Canvas.TopProperty, GetBinding("Y", button));
 
             button.Content = (i == 60 ? 0 : (i == 24 && clockDisplayMode == ClockDisplayMode.Hours ? 0 : i)).ToString(format);
+            button.Tag = Tuple.Create(clockDisplayMode, i);
 
             if (isEnabledSelector is not null)
             {
@@ -428,6 +464,8 @@ private void GenerateButtons(
             canvas.Children.Add(button);
         }
 
+        UpdateButtonAvailability();
+
         BindingBase GetBinding(
             string propertyName,
             object? owner = null,
@@ -444,6 +482,41 @@ BindingBase GetBinding(
     }
 
 
+    private void UpdateButtonAvailability()
+    {
+        foreach (string part in new[] { HoursCanvasPartName, MinutesCanvasPartName, SecondsCanvasPartName })
+        {
+            if (GetTemplateChild(part) is not Canvas canvas)
+                continue;
+
+            foreach (ClockItemButton button in canvas.Children.OfType<ClockItemButton>())
+            {
+                if (button.Tag is not Tuple<ClockDisplayMode, int> item)
+                    continue;
+
+                ClockDisplayMode mode = item.Item1;
+                int value = item.Item2;
+                bool enabled;
+                if (mode == ClockDisplayMode.Hours)
+                {
+                    int hour = Is24Hours ? value % 24 : value % 12 + (IsPostMeridiem ? 12 : 0);
+                    enabled = TimeSelectionRules.Nearest(Time, IsTimeAllowed, hour).HasValue;
+                }
+                else
+                {
+                    var candidate = mode == ClockDisplayMode.Minutes
+                        ? Time.Date.AddHours(Time.Hour).AddMinutes(value % 60).AddTicks(Time.TimeOfDay.Ticks % TimeSpan.TicksPerMinute)
+                        : Time.Date.AddHours(Time.Hour).AddMinutes(Time.Minute).AddSeconds(value % 60);
+                    enabled = TimeSelectionRules.IsAllowed(candidate, IsTimeAllowed);
+                    if (mode == ClockDisplayMode.Minutes)
+                        enabled &= value % 60 % MinuteSelectionStep == 0;
+                }
+                button.SetCurrentValue(IsEnabledProperty, enabled);
+                button.SetCurrentValue(OpacityProperty, enabled ? 1.0 : 0.25);
+            }
+        }
+    }
+
     private void ClockItemDragCompletedHandler(object sender, DragCompletedEventArgs e)
     {
         OnClockChoiceMade(this, DisplayMode);
diff --git a/src/MaterialDesignThemes.Wpf/TimePicker.cs b/src/MaterialDesignThemes.Wpf/TimePicker.cs
index 731cb355e8..9f96660864 100644
--- a/src/MaterialDesignThemes.Wpf/TimePicker.cs
+++ b/src/MaterialDesignThemes.Wpf/TimePicker.cs
@@ -88,7 +88,33 @@ public string? Text
     }
 
     public static readonly DependencyProperty SelectedTimeProperty = DependencyProperty.Register(
-        nameof(SelectedTime), typeof(DateTime?), typeof(TimePicker), new FrameworkPropertyMetadata(default(DateTime?), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTimePropertyChangedCallback));
+        nameof(SelectedTime), typeof(DateTime?), typeof(TimePicker), new FrameworkPropertyMetadata(default(DateTime?), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTimePropertyChangedCallback, CoerceSelectedTime));
+
+    /// <summary>Optional rule for minute slots, used for all selection paths.
+    /// The argument retains its date, with seconds cleared. The rule must be fast and side-effect free.</summary>
+    public static readonly DependencyProperty IsTimeAllowedProperty = Clock.IsTimeAllowedProperty.AddOwner(
+        typeof(TimePicker), new PropertyMetadata(null, SelectionRulesChanged));
+
+    public Predicate<DateTime>? IsTimeAllowed
+    {
+        get => (Predicate<DateTime>?)GetValue(IsTimeAllowedProperty);
+        set => SetValue(IsTimeAllowedProperty, value);
+    }
+
+    /// <summary>Refresh after data captured by IsTimeAllowed changes. Call on the UI thread.</summary>
+    public void RefreshTimeAvailability()
+    {
+        CoerceValue(SelectedTimeProperty);
+        _clock.RefreshTimeAvailability();
+    }
+
+    private static object? CoerceSelectedTime(DependencyObject d, object value)
+    {
+        var picker = (TimePicker)d;
+        return value is DateTime time ? TimeSelectionRules.Nearest(time, picker.IsTimeAllowed) : null;
+    }
+
+    private static void SelectionRulesChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) => d.CoerceValue(SelectedTimeProperty);
 
     private static void SelectedTimePropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
     {
@@ -481,10 +507,14 @@ private bool IsTimeValid(string s, out DateTime time)
     {
         CultureInfo culture = Language.GetSpecificCulture();
 
-        return DateTime.TryParse(s,
-                                 culture,
-                                 DateTimeStyles.AssumeLocal | DateTimeStyles.AllowWhiteSpaces | DateTimeStyles.NoCurrentDateDefault,
-                                 out time);
+        if (!DateTime.TryParse(
+            s,
+            culture,
+            DateTimeStyles.AssumeLocal | DateTimeStyles.AllowWhiteSpaces | DateTimeStyles.NoCurrentDateDefault,
+            out time))
+            return false;
+
+        return TimeSelectionRules.IsAllowed((SelectedTime?.Date ?? DateTime.Today).Add(time.TimeOfDay), IsTimeAllowed);
     }
 
     private string? DateTimeToString(DateTime? d)
@@ -576,6 +606,7 @@ private void InitializeClock()
         _clock.SetBinding(StyleProperty, GetBinding(ClockStyleProperty));
         _clock.SetBinding(Clock.TimeProperty, GetBinding(SelectedTimeProperty, new NullableDateTimeToCurrentDateConverter()));
         _clock.SetBinding(Clock.Is24HoursProperty, GetBinding(Is24HoursProperty));
+        _clock.SetBinding(Clock.IsTimeAllowedProperty, GetBinding(IsTimeAllowedProperty));
         _clockHostContentControl.SetBinding(StyleProperty, GetBinding(ClockHostContentControlStyleProperty));
     }
 
diff --git a/src/MaterialDesignThemes.Wpf/TimeSelectionRules.cs b/src/MaterialDesignThemes.Wpf/TimeSelectionRules.cs
new file mode 100644
index 0000000000..4b10942390
--- /dev/null
+++ b/src/MaterialDesignThemes.Wpf/TimeSelectionRules.cs
@@ -0,0 +1,38 @@
+namespace MaterialDesignThemes.Wpf;
+
+internal static class TimeSelectionRules
+{
+    // Rules describe minute slots; seconds remain available through WithSeconds.
+    internal static bool IsAllowed(DateTime time, Predicate<DateTime>? predicate) => predicate == null || predicate(time.Date.AddHours(time.Hour).AddMinutes(time.Minute));
+
+    internal static DateTime? Nearest(DateTime time, Predicate<DateTime>? predicate, int? hour = null)
+    {
+        if ((!hour.HasValue || time.Hour == hour) && IsAllowed(time, predicate))
+            return time;
+
+        DateTime? nearest = null;
+        long distance = long.MaxValue;
+        long fraction = time.TimeOfDay.Ticks % TimeSpan.TicksPerMinute;
+
+        for (int h = hour ?? 0; h <= (hour ?? 23); h++)
+        {
+            for (int m = 0; m < 60; m++)
+            {
+                var candidate = time.Date.AddHours(h).AddMinutes(m).AddTicks(fraction);
+
+                if (!IsAllowed(candidate, predicate))
+                    continue;
+
+                long delta = Math.Abs(candidate.Ticks - time.Ticks);
+
+                if (delta < distance)
+                {
+                    nearest = candidate;
+                    distance = delta;
+                }
+            }
+        }
+
+        return nearest;
+    }
+}
diff --git a/tests/MaterialDesignThemes.Wpf.Tests/TimeSelectionRulesTests.cs b/tests/MaterialDesignThemes.Wpf.Tests/TimeSelectionRulesTests.cs
new file mode 100644
index 0000000000..cc1d3628ff
--- /dev/null
+++ b/tests/MaterialDesignThemes.Wpf.Tests/TimeSelectionRulesTests.cs
@@ -0,0 +1,135 @@
+namespace MaterialDesignThemes.Wpf.Tests;
+
+[TestExecutor<STAThreadExecutor>]
+public class TimeSelectionRulesTests
+{
+    private static readonly DateTime Date = new(2026, 10, 25);
+
+    private static bool BusinessHours(DateTime time) => time.TimeOfDay >= TimeSpan.FromHours(6)
+        && time.TimeOfDay <= TimeSpan.FromHours(19) && time.Hour != 13 && time.Minute % 10 == 0;
+
+    [Test]
+    public async Task NullRulePreservesOriginalTimeIncludingSeconds()
+    {
+        var time = Date.AddHours(3).AddMinutes(17).AddSeconds(23);
+        await Assert.That(new Clock { Time = time }.Time).IsEqualTo(time);
+        await Assert.That(new TimePicker { SelectedTime = time }.SelectedTime).IsEqualTo(time);
+    }
+
+    [Test]
+    [Arguments(3, 17, 6, 0)]
+    [Arguments(9, 17, 9, 20)]
+    [Arguments(13, 20, 12, 50)]
+    [Arguments(19, 10, 19, 0)]
+    [Arguments(6, 0, 6, 0)]
+    [Arguments(19, 0, 19, 0)]
+    public async Task SelectionIsCoercedToNearestAllowedMinute(int hour, int minute, int expectedHour, int expectedMinute)
+    {
+        var requested = Date.AddHours(hour).AddMinutes(minute);
+        var expected = Date.AddHours(expectedHour).AddMinutes(expectedMinute);
+        var clock = new Clock { IsTimeAllowed = BusinessHours, Time = requested };
+        var picker = new TimePicker { IsTimeAllowed = BusinessHours, SelectedTime = requested };
+        await Assert.That(clock.Time).IsEqualTo(expected);
+        await Assert.That(picker.SelectedTime).IsEqualTo(expected);
+    }
+
+    [Test]
+    public async Task NativeButtonsDisableUnavailableHoursAndMinutes()
+    {
+        var clock = new Clock { Is24Hours = true, IsTimeAllowed = BusinessHours, Time = Date.AddHours(9) };
+        clock.ApplyDefaultStyle();
+        var hours = clock.FindVisualChild<Canvas>(Clock.HoursCanvasPartName).GetVisualChildren<ClockItemButton>().ToList();
+        await Assert.That(hours.Count).IsEqualTo(24);
+        await Assert.That(hours.Count(b => b.IsEnabled)).IsEqualTo(13);
+        await Assert.That(hours.Single(b => b.Content.ToString() == "13").IsEnabled).IsFalse();
+        var minutes = clock.FindVisualChild<Canvas>(Clock.MinutesCanvasPartName).GetVisualChildren<ClockItemButton>().ToList();
+        await Assert.That(minutes.Count(b => b.IsEnabled)).IsEqualTo(6);
+        clock.Time = Date.AddHours(19);
+        await Assert.That(minutes.Count(b => b.IsEnabled)).IsEqualTo(1);
+    }
+
+    [Test]
+    [Arguments("3:17", false)]
+    [Arguments("9:17", false)]
+    [Arguments("13:20", false)]
+    [Arguments("19:10", false)]
+    [Arguments("9:20", true)]
+    [Arguments("19:00", true)]
+    public async Task ManualInputUsesTheSameRule(string text, bool accepted)
+    {
+        var picker = new TimePicker { Is24Hours = true, IsTimeAllowed = BusinessHours, SelectedTime = Date.AddHours(9) };
+        picker.ApplyDefaultStyle();
+        var input = picker.FindVisualChild<TextBox>(TimePicker.TextBoxPartName);
+        input.Text = text;
+        input.RaiseEvent(new RoutedEventArgs(UIElement.LostFocusEvent));
+        await Assert.That(picker.SelectedTime).IsEqualTo(accepted ? Date.Add(TimeSpan.Parse(text)) : Date.AddHours(9));
+    }
+
+    [Test]
+    public async Task ManualInputRuleReceivesTheSelectedDate()
+    {
+        var picker = new TimePicker { Is24Hours = true, SelectedTime = Date.AddHours(9), IsTimeAllowed = t => t.Date == Date };
+        picker.ApplyDefaultStyle();
+        var input = picker.FindVisualChild<TextBox>(TimePicker.TextBoxPartName);
+        input.Text = "10:20";
+        input.RaiseEvent(new RoutedEventArgs(UIElement.LostFocusEvent));
+        await Assert.That(picker.SelectedTime).IsEqualTo(Date.AddHours(10).AddMinutes(20));
+    }
+
+    [Test]
+    public async Task RefreshReevaluatesCapturedBookings()
+    {
+        var booked = new HashSet<TimeSpan>();
+        var clock = new Clock { Time = Date.AddHours(9), IsTimeAllowed = t => BusinessHours(t) && !booked.Contains(t.TimeOfDay) };
+        clock.ApplyDefaultStyle();
+        booked.Add(TimeSpan.FromHours(9));
+        clock.RefreshTimeAvailability();
+        await Assert.That(clock.Time).IsEqualTo(Date.AddHours(8).AddMinutes(50));
+    }
+
+    [Test]
+    public async Task EmptyAvailabilityClearsPickerAndDisablesClockButtons()
+    {
+        var picker = new TimePicker { SelectedTime = Date.AddHours(9), IsTimeAllowed = _ => false };
+        await Assert.That(picker.SelectedTime).IsNull();
+        var clock = new Clock { IsTimeAllowed = _ => false };
+        clock.ApplyDefaultStyle();
+        var hours = clock.FindVisualChild<Canvas>(Clock.HoursCanvasPartName).GetVisualChildren<ClockItemButton>();
+        await Assert.That(hours.Any(b => b.IsEnabled)).IsFalse();
+    }
+
+    [Test]
+    public async Task RemovingRuleRestoresAvailabilityAndPreservesExistingMinuteStep()
+    {
+        var clock = new Clock { Time = Date.AddHours(9), MinuteSelectionStep = 15, IsTimeAllowed = _ => false };
+        clock.ApplyDefaultStyle();
+        clock.IsTimeAllowed = null;
+        var minutes = clock.FindVisualChild<Canvas>(Clock.MinutesCanvasPartName).GetVisualChildren<ClockItemButton>();
+        await Assert.That(minutes.Count(b => b.IsEnabled)).IsEqualTo(4);
+    }
+
+    [Test]
+    public async Task DraggingCannotSelectAnUnavailableMinute()
+    {
+        var clock = new Clock { IsTimeAllowed = BusinessHours, Time = Date.AddHours(9), DisplayMode = ClockDisplayMode.Minutes };
+        clock.ApplyDefaultStyle();
+        var canvas = clock.FindVisualChild<Canvas>(Clock.MinutesCanvasPartName);
+        double center = canvas.Width / 2;
+        double angle = 17 * Math.PI / 30;
+        clock.RaiseEvent(new DragStartedEventArgs(center + Math.Sin(angle) * center * .8, center - Math.Cos(angle) * center * .8)
+        {
+            RoutedEvent = ClockItemButton.DragStartedEvent
+        });
+        clock.RaiseEvent(new DragDeltaEventArgs(0, 0) { RoutedEvent = ClockItemButton.DragDeltaEvent });
+        await Assert.That(clock.Time).IsEqualTo(Date.AddHours(9).AddMinutes(20));
+    }
+
+    [Test]
+    public async Task RejectedMeridiemChangeKeepsHeaderConsistentWithTime()
+    {
+        var clock = new Clock { IsTimeAllowed = t => t.Hour >= 14 && t.Hour <= 18, Time = Date.AddHours(14) };
+        clock.IsPostMeridiem = false;
+        await Assert.That(clock.Time).IsEqualTo(Date.AddHours(14));
+        await Assert.That(clock.IsPostMeridiem).IsTrue();
+    }
+}