2 hour call out, most bases have 0400-1600 and 1100-2300 availability periods but some have other 12 hour-ish reserve periods.

They can swap your reserve period within your block of days but have to ask you first on your first or last day since it wasn't in your original foot print.

Days work is highly dependent on base and month to month. Can pick up on your days off but only if FARs for duty and flight times aren't limited for your next reserve period.

Can get critical pay(200%) if you accept an assignment on a day off and you're legal(but they will try and get you to swap your day off first instead of critical pay)

I've averaged around 4-8 days a month flying on reserve but my base has a pretty low call out rate and is very isolated from the other bases.

If you live in base, it's not too bad at some places(again, base and month dependent). If you commute, I'd recommend just doing virtual base and make the company pay for your hotel until you can get a line.