Most clinics have their own post op protocol but after my procedures I wore one loosely straight afterwards. I would wait at least 10 to 12 days before tightening the hat in my opinion, this also depends on whether it's FUE or FUT. It's a good idea to wait until the staples/sutures are out so as not to aggravate the sutures/staples if worn too tight.
Warm wishes bullitnut