DD2 is 8 weeks and I change her nappy at about 10 before bed and not again until the morning (unless it's soloed, of course). I've been doing this since about week 2, it's always very full in the morning but had never leaked.
IIRC I used to change DD1s nappy a couple times during the night for the first few months but I can't remember why?!
When did you let them go all night with the same nappy?