max for me is 8-9 hours, and I also use plastic / vinyl pants on top to help reduce odor.
In a month though, on my work we will have a teamday which is supposed to last 11-12 hours, in which I have no chance of changing my diaper, so that will really push it to the limits....but usually lots of babypowder helps and I plan on only drinking water that also cut's down the smell of a wet diaper..