How quickly strings "die" is a function of the construction of the strings, how much you play, and your body chemistry. It's also a function of what kind of sound you're wanting. If you go for a darker, bassier tone then you can leave 'em on a lot longer. Heck...I know a guy here in town that plays in a Motown cover band and goes for a real string-bass kind of sound. He's got a 1974 Fender Jazz bass that he bought new, and it still has the original strings!!!!
I kill bass strings left and right. After 8-10 hours of play time...they're gone as far as I'm concerned and they get changed. But, I'm going for a really bright, ringing tone (think Chris Squire or Geddy Lee).
I really like D'Addario strings (I use them on almost all of my electric guitars), but for some reason I got no life out of their bass strings.
I've been using Dean Markley Blue Steels for years now, and I can get maybe 3 shows out of them (that's 9 one-hour sets). I just tried some new Ernie Balls on the last change...and they seem to be holding up pretty well so far.
If you've got 3+ months at 3 or 4 hours a day on the strings...that's a lot of playing time.
The only other thing I would add is to make sure that you wash your hands before you start playing, and wipe the strings down as soon as you're done.
Greetings from Austin, TX
Ken