I took your and others' suggestions to try BusyCal, downloaded the free trial and overall liked it, enough that after a couple of weeks decided to go ahead and purchase it ($49)... all good. Then just TWO days later got notice from them of a new version, available to all users (old and new) for $29 from the Apple app store. I griped that given I'd only just paid for the old version and wondered if they could give a free upgrade. Instead they gave me a full refund and said I should just buy the new version. Not what I'd asked for but arguably a better deal.
BUT.... then I looked into the new version and saw that it is designed to integrate with Mountain Lion Notifications! In other words: THE SAME SNOOZE DEFICIENCIES. No option for snooze duration at all... I believe you can set a default snooze length, but that's it.
So I wound up re-purchasing the OLD BusyCal, version 1.6, and will again wait out whatever time for Apple to add a customizable snooze back in... or until something better comes along that integrates smoothly with Mail and Safari.