i would wait 2 weeks minimum, but ideally atleast 3-4 weeks...for future reference if you know you're going to get a sew in there's no reason to relax your whole head, because most of it is going to be hidden, and you're just weakening the strands that are about to be braided and the hair is going to be sewed on to...if you're getting a touch up, just to around the edges or the leave-out...and if its a full head with no hair out, you dont need to relax at all.