diff --git a/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs b/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
index 3ff9d7e..b71b22e 100644
--- a/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
+++ b/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
@@ -345,20 +345,28 @@ public sealed class TimetableViewModelTests
     public async Task OpenWeekCell_LessonHeuteWaehrendUnterrichtszeit_OeffnetUnterrichtsmodus()
     {
         var group = new LearningGroup { Name = "Q1 Chemie" };
-        var today = DateOnly.FromDateTime(DateTime.Today);
+        // Bewusst nicht der reale DateTime.Today-Wochentag: an einem Sa/So gäbe es dafür keine
+        // Kachel im Mo-Fr-Raster. Stattdessen ein beliebiger Wochentag der laufenden Kalenderwoche
+        // (Kachel existiert immer), dessen Datum per VM.Clock als "heute" simuliert wird (siehe
+        // TimetableViewModel.Clock - genau für solche Tests eingeführt).
+        var weekday = DayOfWeek.Monday;
+        var lessonDate = DateInCurrentWeek(weekday);
         var slots = new FakeTimetableSlots();
-        slots.Add(new TimetableSlot { GroupId = group.Id, Weekday = today.DayOfWeek, PeriodNumber = 1 });
-        var lesson = new Lesson { GroupId = group.Id, Date = today, LessonNumber = 1, Topic = "Redox" };
+        slots.Add(new TimetableSlot { GroupId = group.Id, Weekday = weekday, PeriodNumber = 1 });
+        var lesson = new Lesson { GroupId = group.Id, Date = lessonDate, LessonNumber = 1, Topic = "Redox" };
         var lessons = new FakeLessons();
         lessons.Add(lesson);
         var periodSchedule = BuildPeriodSchedule(1);
         var vm = BuildViewModel(slots, new FakeGroups([group]), lessons: lessons, periodSchedule: periodSchedule);
+        // Gleiche Uhrzeit wie BuildPeriodSchedule (reales DateTime.Now), aber am simulierten
+        // "heutigen" Datum - die Stundenzeit-Prüfung (Uhrzeit) bleibt so unabhängig vom Datum.
+        vm.Clock = () => lessonDate.ToDateTime(TimeOnly.FromDateTime(DateTime.Now));
         Lesson? teachingModeLesson = null;
         Lesson? viewerLesson = null;
         vm.OnOpenTeachingMode = l => { teachingModeLesson = l; return Task.CompletedTask; };
         vm.OnOpenLessonViewer = l => { viewerLesson = l; return Task.CompletedTask; };
 
-        var cell = vm.WeekItems.Single(c => c.IsSlotCell && c.Weekday == today.DayOfWeek && c.PeriodNumber == 1);
+        var cell = vm.WeekItems.Single(c => c.IsSlotCell && c.Weekday == weekday && c.PeriodNumber == 1);
         await vm.OpenWeekCellCommand.ExecuteAsync(cell);
 
         Assert.Equal(lesson.Id, teachingModeLesson?.Id);
diff --git a/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs b/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
index 2560bff..e6c30a3 100644
--- a/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
+++ b/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
@@ -109,6 +109,11 @@ public partial class TimetableViewModel : ObservableObject
     public Func<Lesson, Task>? OnOpenLessonViewer { get; set; }
     public Func<Lesson, Task>? OnOpenTeachingMode { get; set; }
 
+    /// Öffentlich statt intern (kein InternalsVisibleTo in dieser Codebasis) - erlaubt Tests, die
+    /// "heute"-abhängiges Verhalten (Wochenraster-Badges, Unterrichtszeit-Erkennung) prüfen, ohne
+    /// vom tatsächlichen Wochentag/der Uhrzeit im Testlauf abzuhängen.
+    public Func<DateTime> Clock { get; set; } = () => DateTime.Now;
+
     public TimetableViewModel(ITimetableSlotRepository slots, IGroupRepository groups,
         ISubjectRepository subjects, ILessonRepository lessons, IExamRepository exams,
         ISchoolHolidayRepository schoolHolidays, SchoolCalendarSettingsService calendarSettings,
@@ -156,7 +161,7 @@ public partial class TimetableViewModel : ObservableObject
 
     public void Load()
     {
-        var today = DateOnly.FromDateTime(DateTime.Today);
+        var today = DateOnly.FromDateTime(Clock());
         TodayLabel = today.ToString("dddd, dd.MM.yyyy", System.Globalization.CultureInfo.GetCultureInfo("de-DE"));
 
         var publicHolidayDates = new HashSet<DateOnly>();
@@ -399,9 +404,10 @@ public partial class TimetableViewModel : ObservableObject
     private static readonly TimeSpan TeachingTimeTolerance = TimeSpan.FromMinutes(10);
     private bool IsAroundTeachingTime(DateOnly lessonDate, int periodNumber)
     {
-        if (lessonDate != DateOnly.FromDateTime(DateTime.Today)) return false;
+        var nowSnapshot = Clock();
+        if (lessonDate != DateOnly.FromDateTime(nowSnapshot)) return false;
         if (_periodSchedule.GetTimes(periodNumber) is not { } times) return false;
-        var now = TimeOnly.FromDateTime(DateTime.Now);
+        var now = TimeOnly.FromDateTime(nowSnapshot);
         return now >= times.Start.Add(-TeachingTimeTolerance) && now <= times.End.Add(TeachingTimeTolerance);
     }