I agree that drinking water to keep your urine clear is a good way to reduce odor. Urine will start to smell after a while, so don't keep a wet diaper on in public for too long... unfortunately, I can't really give a set amount of time that a diaper will start to smell. I've had it where it starts to smell an hour after wetting (I was dehydrated, it was hot outside, and I was active), and I've also gone 8+ hours with nary a smell (I was sleeping and it wasn't hot or humid).
Granted, this is my nose trying to pick up my own body odors, so it might not be the most accurate gauge, but... there comes a point where even I start to get offensive to myself, so I figure that the point at which I am offensive to others happens before that. But yeah, there's something to be said for disposables and their ability to lock in urine smells. It seems the ones that have a fair bit of gel in them do best with this. I had some older Attends with no gel in them, just pulp and... never again. Reeked after only an hour or so without it being hot out or me being active.