Tell them upfront how it works. Get them to sign the paper that they know how it all works.
I can't really agree with the second part of this statement. In 16 years photographing weddings I find that doing a good job and working with your customer is the way to succeed. I agree that it's good to explain how you normally work, but is it really necessary to get them to sign a contract with too many small details? Not questioning your way of working personally, but there is a school of thought with wedding photographers that contracts and Term's and Conditions need to cover everything, and quite often they become very skewed toward what suits the photographer rather than providing a good service. I have already admitted above that my editing times do slip, but let's face it, except in extenuating circumstances or unless you are going on holiday the day after the wedding, then there is no logical reason not to edit the pictures within a week of the wedding.