Having sat reserve at a regional and now at a Legacy, the 2 are night and day different. At US, Reserve is quite human. In fact, a lot of people bid reserve that could hold blocks. On my airplane (767 International), reserve is a great place to hide out in the winter (due to lack of activity on the fleet). I hold long call which is 12 hours to check-in. If it's a Domestic departure, check-in is 60 minutes prior. International is 90 minutes prior (going to 60 eventually). Our reserve system is very transparent. We use a bucket system and it's based on Least Time Order. I can look to see where I sit on the reserve list and what trips are available. The block holders can trip improve 2 days prior, so that gives you a good idea of what will be open for your days on. Future Scheduling processes Long Call Reserves at 1:00 pm (Pittsburgh Central Time) the day prior. I sat the entire week of New Years as wasn't called once. I've been called a few times in January. No telling yet for February.
Trips range from out and backs to the islands (or ORD), ferry flights, the handful of domestic we have out of PHL and 3-day (sometimes 4 with winter schedules) International trips. The big downside is the 757 can equipment sub for just about any airplane in the fleet, so you have to watch that.
They can transition you to short call if they don't have enough short call reserves, but Scheduling is pretty good at assigning a later RAP. Also, if you're long call, you don't go on until midnight your first day. Future can call you with a trip for your first day on your off day, but you're under no obligation to answer until midnight. I sit long call from DFW and I'm based in PHL. So far so good (knock on wood).
At XJT, it was as described above. I didn't sit reserve there long. When I did, it was feast or famine. Some months I flew a ton, others I hardly flew at all.