When I'm jamming at home or learning songs, it doesn't bother me if the strings are old. In fact several of my nice guitars that I don't gig with will go many months before I change the strings. But usually the guitars I gig with go about 1-2 weeks tops before I change 'em. Like if I put new strings on my go to axe on Wed or Thurs, play Friday and Saturday and then have a gig the following weekend, I'll change them on Wed/Thurs again. If not, I probably wait 'til the following week (I never get more than 1 weekend off in a row).