Expressjet:
I can only really give you accurate estimates for Newark. The other bases are a guess based on what I hear.
EWR: 3-5 months and increasing (base is shrinking)
IAH: at least 4 months (our biggest base, which for some odd reason everyone seems to want)
CLE: About 9 years. (just a joke, but rsv times there are rather long from what I gather)
I don't know much about the branded and Delta bases, but I gather rsv in LAX is pretty short. The good news is that our work rules are good and being on reserve really isn't bad at all. At least if you live in base. Commuting to be on reserve will suck anywhere.