If you're fortunate you'll get the 175 in new hire class, which I've heard has reserves that are actually used and a relatively short time on reserve before you hold a line. The fleet is expanding as well, with several aircraft on the way through 2020. More flying equals more options and comforts when it comes to picking lines each month.
If you're like most people though, you'll be on the 145. In either ORD or LGA. At the moment either base is overstaffed on the FO side of the 145, with reserves not being used much, and a much longer time spent on reserve overall.
If you live in base, you will spend the first month or two mostly on airport standby, sitting in the crew lounge for 8 hours a day until you get called or they send you home. After this initial time you'll move to receiving 14 hour RAPs, which start at 4AM or 10AM. These RAPs have a two hour call out window, unless you are in NYC where you get 3 hours to show.
Reserve lines are set up in 4 on, or 5 on sets of days working, with 11 days free from work altogether.
If you commute while on reserve, you will most likely need a crash pad. You will spend your 4/5 days out of the week waiting for work, and probably only get called once or twice for a low time turn. The RAP that starts at 4AM will be mostly uncommutable the same day, but it does end at 6PM, leaving you with options to go home. If you start on the 10AM RAP you'll be able to come in easy enough but getting home will be an issue as that one doesn't end until midnight.
If you call crew scheduling you could potentially get out of either RAP or standby shift early, staffing permitting. You'll have better chances as you gain seniority.
On your first day of a set of reserve days you'll most likely be preassigned a 4AM RAP. You'll still be legal for the 4 or 10AM shift the next day however, so what crew scheduling will give you might be hard to predict. If you do end up on a 10AM RAP, you will only be legal for subsequent 10AM RAPs unless scheduling can let you out early from a 10AM RAP so you can legally ask for the 4AM shift.
There is a "proffering" system in place for reserves, where you tell scheduling which shift you prefer to work the next day. If there are trips open the next day they can also be requested in lieu of working a reserve shift. This is all seniority based of course.
Once you DO get a line, you'll be stuck with mostly 11/12 day off lines until you can hold better. At the tail end of your stint as an FO you'll be holding 15-17 day off lines. Once you upgrade you get to repeat the reserve process. We've got a high number of FOs due to upgrade in the next year so there's a chance the CA seat won't be so understaffed, leading to a better QoL on reserve overall.