30 to 45 minutes is the longest I've gone, I think. I usually change after about 15 minutes. And for me it can change the way that the diaper absorbs urine. Like Spokane Girl said, the poop isnt absorbent, so the pee can trickle off the sides of the load or even into the back. This isnt too uncommon if I have had to sit down in the mess and stand up to go change. Fortunately the leg gathers stop the pee from getting out in this situation, as long as the diaper isnt already about to leak.
I have male plumbing down there, but I tuck it downwards very snug, and it doesn't move at all, so I do pee more downward. This does make a leak slightly more likely while messy, but the benefit of being able to pee into the core of the diaper, and not have to worry about it getting "loose" and draining into a weak spot around the tapes, outweighs the risks.