The time module automatically calculates whether a time entry needs to be overtime or regular time.  There are a variety of overtime policies.  The most common is Overtime after 40 hours a week, with the second most common overtime after 8 hours in a day and after 40 hours in a week.   Some departments or agencies have other policies such as double time on Sundays.   You can create a custom policy in the overtime module.  Comp time can also be addressed appropriately in the Overtime selector, as comp time carries regular time fringe rates, not overtime fringes.