The Service Hours to Date field in the Pay Details on the employee record is a running total of the hours worked by the employee since their record was created. It updates as part of the End of Pay process, with the Normal and Leave hours included in the pay period.
You cannot change the hours included; e.g. you cannot select hours paid via additions or use hours worked leave to accumulate the Service Hours to Date. And the Service Hours to Date cannot be used to accrue leave.