Writing a PCR with using standard operation and functions is considered as standard 
In order to check cumulated hours, you can use HRS=M then follow by your time type. In B2 cluster it's SALDO table. To retrieve it, please using HRS=M.
You can see how I use the operation in Carry Forward Absence Quota | SCN
or https://scn.sap.com/docs/DOC-47492
Good luck.
Woody (Trong Minh)