Hi Dinx
Noah wakes roughly every 3 hours in the night to feed and we have tended to change him each time before I feed him. We have just started peeking into his nappy now to see if it is dirty. if it is he gets changed, but if not we leave him. My HV said that a wet nappy can be left longer, but does need changing if it's dirty.
H has a teeny pocket torch he uses to peer inside the nappy 
N also sleeps in Grobags so I know what you mean about the faff of getting him undressed. I find that N tends to feed back to sleep though, hence changing before feeding rather than after.
HTH
x