Hi,
Check the standard schema part which will give you an idea that how schema is working.
In the time management schema is running on daily basis from Day beginning and Day End. And inside that it's checking Input details of Time Entry, Then Evaluate Time Entry , Then Over time calculation, Then generate leave balances etc.
Whenever you will design your schema you will copy the standard schema and your custom PCR will incorporate inside the Z schema where it's required means and for that you have to understand each block of the time schema processing.
Regards,
Sankarsan