Nappies at night, when to stop?

our son will be 3 years old in 6 days time and we have started potty training him a week ago. there have been no accidents at all in 5 days. we put a nappy on him at night but when he gets up in the morning it is bone dry and once he gets out of the bed he tells me he wants to go pepe, we go to the bathroom i take the nappy off and he does a big pee in his potty. given that he is holding his pee at night, for how much longer should we keep putting a nappy on him (just in case) before just letting him go to bed with a boxershorts under his pj bottoms? we were thinking that if he is still holding his pee all night for another two weeks we should stop using nappies at night, or would it be ok to stop sooner or better to leave them on him for longer just in case. what do you think?