You don't need to change it the second it gets wet... if your worried about diaper rash just always put talcom powder and diaper rash cream on him every 2nd or so change.
I do this and my son has not once had diaper rash, he wets like crazy, sleeps long periods overnight and is soaked in the morning, but i swear hes never had diaper rash, i put that down to keeping his bits clean and protected at all times.