How long do dealerships allow for pre-purchase inspection?

Never done this before. Called dealership and verified they allow Pre Purchase Inspection off site. They confirmed.

Called a nearby mechanic with good reps who confirmed they do PPI. He said it would have to be dropped off for a "few hours." Said the inspection itself would only be 15-20 minutes, but give them a window because they're working on lots of vehicles...that seems like a long time for a dealership to feel comfortable with having a car gone with a potential buyer????? He said in his opinion if they're not comfortable with it, it's not the place to buy from lol.

Is this normal or am I missing something?

I am trying to coordinate from over and hour away and not from the area where purchasing, but I can try to locate other mechanics. I was trying to make sure it was close in relation to the dealership, and having some difficulty between that and making sure they're both reputable and do PPI....little harder than expected. But I can go back to the drawing board if "hours" is not gonna fly.