Membrane sweep at 39 weeks

So I had an appointment today and I will be 38 weeks tomorrow. My midwife mentioned that they can get membranes swept at 39 weeks and my next appointment is next Friday so I’ll be 38+6. Do you know if you have to be exactly 39 weeks or will they let it slide since it’s just a day off? Never had mine swept before so I don’t really know if they’re strict about that or not. Also for those that have had their membrane swept did it help you and how long after did you go into labor? My first came at exactly 38 weeks so I never had the opportunity to get that done.