Collision Checks in Time Management 
Data records often overlap in Time Management. These overlaps are known in the SAP system as collisions.
When you enter new time data, the system checks for collisions with existing Time Management records; as it does for new master data.
These collision checks guarantee that payroll accounting runs smoothly, as well as allowing the system to present a comprehensive and accurate history of time data.

Please note that collision checks in Time Management do not serve the same purpose as time constraints in master data.