It's varies, by a lot. If you're trying to crack an individual account, it may not be crackable at all, and if it is, it might take up to 10k passwords to go through, which takes a lot longer than you think. If you're cracking a list of lets say ~2000 alts, it could get you anywhere from 1-2000 alts, it is 100% dependent on your password list. Bigger the list, longer it takes.
- - - Updated - - -
You can use Weepcraft's free scraper, or you can google dork for pastebin lists and check them. There are many external programs and methods available, but those are the 2 I use.
:P