Since gut doesn't lose as much tension as other strings, and maintains a lot of resiliency over time if stored correctly, I don't see any reason a flat hitter shouldn't get months of time out of a gut string job, even if the player plays fairly often and hits hard. I've got 4 months on my gut/poly string jobs and the gut is barely frayed and playing great. I keep putting in stringsavers around the edges of the stringbed to make up for the poly tension loss. I play several times a week and hit harder and probably flatter than almost anyone on this board.
If you look at the classic racket forum, you will find instances where someone finds an old racket strung with gut that hadn't been played with for years and it hits just fine. In other cases, the strings don't respond well - it depends on how it is stored.
The gut is your friend. Take care of it.