That is a bit of a loaded question in many ways. Work rules/lines are different at every airline. I've been with my airline for 4 years and I still don't understand many parts of the contract. So a summary here would be pointless. Reserve times, well they vary by every airline and within every airline at each base and equipment.

Comair typical f/o reserve times are:
CVG CRJ: 18 months
JFK CRJ: 6 months
CVG CR7: 24 months
but these are very dynamic