diff --git a/src/Services/Scheduling/Application/Features/TimeSlots/Commands/AddTimeSlot/AddTimeSlotCommandValidator.cs b/src/Services/Scheduling/Application/Features/TimeSlots/Commands/AddTimeSlot/AddTimeSlotCommandValidator.cs
index f4a2bec3..2060e74b 100644
--- a/src/Services/Scheduling/Application/Features/TimeSlots/Commands/AddTimeSlot/AddTimeSlotCommandValidator.cs
+++ b/src/Services/Scheduling/Application/Features/TimeSlots/Commands/AddTimeSlot/AddTimeSlotCommandValidator.cs
@@ -22,6 +22,19 @@ public AddTimeSlotCommandValidator(ITimeSlotRepository timeSlotRepository)
             .MustAsync(TimeSlotNameUnique)
             .WithErrorCode("TSNU001")
             .WithMessage("An group with the same name already exists.");
+
+        RuleFor(addTimeSlotCommand => addTimeSlotCommand.StartTime)
+            .NotEmpty()
+            .NotNull();
+
+        RuleFor(addTimeSlotCommand => addTimeSlotCommand.EndTime)
+            .NotEmpty()
+            .NotNull();
+
+        RuleFor(addTimeSlotCommand => addTimeSlotCommand.EndTime)
+            .GreaterThan(addTimeSlotCommand => addTimeSlotCommand.StartTime)
+            .WithErrorCode("TSEV001")
+            .WithMessage("EndTime must be after StartTime.");
     }
 
     private async Task<bool> TimeSlotNameUnique(string name, CancellationToken token)
diff --git a/src/Services/Scheduling/Infrastructure/Repositories/TimeSlotRepository.cs b/src/Services/Scheduling/Infrastructure/Repositories/TimeSlotRepository.cs
index 77466644..8a0dee66 100644
--- a/src/Services/Scheduling/Infrastructure/Repositories/TimeSlotRepository.cs
+++ b/src/Services/Scheduling/Infrastructure/Repositories/TimeSlotRepository.cs
@@ -19,7 +19,7 @@ public async Task<IReadOnlyList<TimeSlot>> PagedAsync(IPaginationFilter paginati
         int skip = (paginationFilter.PageNumber - 1) * paginationFilter.PageSize;
 
         return await _dbContext.Set<TimeSlot>()
-        .OrderBy(timeSlot => timeSlot.Name)
+        .OrderBy(timeSlot => timeSlot.EndTime).ThenBy(timeSlot => timeSlot.StartTime)
         .Skip((paginationFilter.PageNumber - 1) * paginationFilter.PageSize).Take(paginationFilter.PageSize)
         .ToListAsync();
     }