That would make sense and the only reason I can see for waiting. Or if he was on a medication like a blood thinner...then they'd have to wait too.
True had back my father off Coumadin when he had surgery.
Generally, he would have to go off the thinner about 7 days or so both before and after an operation.
Of course, there are exceptions such as dire emergency surgery.
Leni
My wife's a pharmacist and she told me that if he's on blood thinners, depending on the dose, that it would be best to get off them a few days ahead of surgery.