Q1:
Depends what you want:
1) You can use only Work center-> Planing->Absences and Absence->Update to insert it in WC Calendar
2) You can use Registered Absences, Implement Registered Absence after that and Work center-> Planing->Absences...
3) You can also use Reg. Abs. (from Work Center) for more dates absences in one time, Implement Registered Absence after that and Work center-> Planing->Absences...
Q2:
Released PO will not be rescheduled by system. You need to refresh these production orders to affect these absences changes.
