Hey there SlapPopBass. I think maybe your poll is a bit lawed. Now before you get all upset at me, let me explain. IMHO, I don't think there isn't a "time period" in which to change strings. Strings should be changed out when needed. For instance, if you want that "zing" of fresh strings you should change them when the "zing" is gone. If you want a good "dub-dub" tone that only well worn flat wounds can produce, then you shouldn't change them at all. (unless broken)
With that said, most commercial string manufacturers will tell you that you will only get about 20 to 30 hours out of a set of nickel round wound strings before they are pretty much dead. In my experience, Circle K strings will out last that by at least 2 to 3 times and so will coated strings. SS strings will go a bit further than most nickel strings, but won't be as bright out of the box. Still, they won't last more than about 40 hours before they lose their brightness and attack.
If you are recording a song and are anal about your tone (ala John Entwistle) you'll change your strings after every take. LOL.....
Of course, I say all of this with the understanding that it is all subjective and that this is my opinion. If you think your bass is starting to sound like crap, change the strings out and you'll find that tone you always liked about your bass when you bought it.
Peace.
Rob C
Arizona Bass Company