Real-Time Overlap Prevention (Client Side)

You can enable real-time overlap checking using AllowEventOverlap property.

Server Side

1. Typically, the check will need to be done in EventResize, EventMove. Depending on how you create the new events you might need to add it to TimeRangeSelected, TimeRangeMenuClick, TimeRangeDoubleClick, and Command.
2. You can use the following SQL select to check the new date: Testing for Overlapping Events with SQL
3. If the new/updated event doesn't meet the criteria, you should deny the action (don't update the DB) and notify the user using UpdateWithMessage(msg):

Event handler (.aspx.cs file):

DayPilotScheduler1.UpdateWithMessage("This action is not allowed (overlapping events)");

This technique is also demonstrated in the Hotel Room Booking Scheduler Tutorial.