I agree with mazzic on this one. I recently had to change over to 12hr shifts as a security patrolman. Lots of time stuck in a car, and walking around - pretty much non-stop for 12 hours straight.
I kept up with my training though, and it sucked major ass at first. But, after a couple of weeks, you just get used to it. Your body is crazy at adapting to its environment - I think you will be pleasantly surprised in the long run.