Is it OK to wear a cap 5 days after FUE hair transplant?

You can usually wear a cap or a hat on the same day of surgery but if you are concerned you should check with your doctor.

Some doctors would say wait a week. In general make sure the cap is loose and be mindful when you're taking it off and putting it on and your transplants should be alright.

Wearing
a loose fitting hat at 5 days is fine. Try not to let the cap rub on the
recipient area until about 10-14 days after surgery. Also be careful putting
the cap on and taking it off so you don't inadvertently rub out some of the
grafts. 

10 days following the hair transplant procedure when the scabs in the recipient area has fell off, you are allowed to wear a cap (wool caps or similar hats are not allowed.

You can wear a hat at 5 days provided that it does not rub on the recipient area or the donor area. Make sure it is not tight