Combining compensatory absence and normal hours on time card

Content

Hi, can anyone point me in the right direction please as I am quite new to the T&L module. 

We are having a problem where employees cannot enter some hours on a day in the time card as well as there being some absence hours. 

For example, if the employee had already booked 4 hours off via Absence Management (hours deducted from the Compensatory absence plan balance) these 4 hours show by default on the Time Card for that week. However, if they actually worked 4 hours on the same day (effectively they had a half day off), when they come to submit the Time Card  they are getting an error message about overlapping time entries.