So that is 2 gigs (4x45). I don't think I could ever get 2 gigs out of a set of strings. I saw off D strings playing rhythm. I use 10-46 and for a while I was buying a bunch of 28s to substitute for the Ds until I found out the core size was the same for both.
I put a new set on for every gig and perform the stretching ritual and still end up horribly out of tune by the end of the first song. After that it settles down.
I think it takes 6 minutes, not 6 hours before the tone changes noticeably. Once you get the first stretch out of them, there is that first plateau on the way to shittiness. They sound about like that for as long as you play *that night*.
After one heat cycle, they go to the second plateau, which is couch pickin', dull n' rusty. The good part is, that strings stay at this plateau for the rest of their lives - or until they break. I pull guitars out of cases that have perfectly petrified strings on them. You can immediately pick it up and play anything but slide (sounds like a cat trying to dig a rubber band out of a paper grocery bag it's so scratchy). Just make sure you wear your safety goggles when bending more than a half step. I wonder if that old Hondo II is still in the crawlspace.
I always record rhythm guitar with the petrified strings because the tone is much better than a brand new set of jangly ernie balls. Less string noise, too. When I record leads, I may break down and restring for the sake of intonation, but ideally, the strings record best within a couple days after the last gig.
So, how often to change them? Only when they really start to bug you, or where your fingers look like they have nicotene stains on them from your rustocaster practice.
Unless you're talking about acoustic strings, which puts you (unless you play in a cleanroom wearing gloves) back to "every hour on the hour".