When hiring a new employee, the values (% and Hrs) should default from IT0007 since you are creating an IT0008 with the same start date, IF you have activated the appropriate parameter, but during other actions, it will not work if IT0008 is "Copied".
Since we have some very special "part-time" periodic work schedules, our ABAP resource added 2 fields on table PA0007, and did some programming so that these fields would be filled with the value of field M2STD from V_T508A (where we enter the percentage or cap.utilisation level), and the number of working hours per pay period (hours per week x 2 x %).
We deleted IT0008 from our actions, and created a Dynamic Action (table T588Z) so that when an IT0007 is saved, the IT0008 is copied with the same Start Date, % and Hrs as in IT0007.