2 hours is still a lot longer than 5 minutes. Rapid turnover is important for these folks. I've seen rental companies run out of cars numerous times. Two hours is tough. Plus, how about when dozens of cars have been turned in and are waiting on a charge? If anything, they are most likely to levy a higher fee for returning uncharged because of their lost time.
It would seem ideal to have the line-up area where cars are turned in, inspected and cleaned set up with a bunch of retractable charger leads in the ceiling, ala shop air. As soon as you pull up, the attendant pulls down a lead and plugs the car in. Bam.