About 10mins is right.
There’s a free drop off you can wait at (not sure how long you’re allowed to wait before they charge you) and your friend will get bussed to it for free or you can pay £1 to use the paid drop off right in front of the terminal (although the charge goes extortionate after 15mins)
Don’t think there is anything to stop you waiting at the free drop off and going for a drive around the airport if you run out of free time before going back. Alternatively you could wait in the Ingliston P&R car park at the top of the airport road / Newbridge village / Ratho station for free until your friend phones to stay he’s escaped passport/customs control.