By far the best way is to have a child table of services performed.
One Work Order Has Many Services Performed. The data entry can be by grid edit.
That will allow full flexibility on calculating employee hours. It also allows for the granularity that not all the a services performed on a work order may not all be on the same day, and hence may cross a pay period. if the hours are entered for any given date, then that will not be a problem.