2:25pm flight. Pulled in to this facility (which is not the easiest to find) at 12:48pm. Uh oh......
Went around to the Dollar section, pulled in, got the car scanned, walked to the shuttle and was at McCarran at 1:10pm. BOOM! POW! Well done, Rent-a-car Center! A seamless check-out process (I can't speak for all the other companies that are represented there, but I assume they follow the same check out process as Dollar) and a timely shuttle schedule gives you no excuse for missing your flight.
The facility itself has an AC's indoor area and has eateries, but who needs em! It's a quick in/out. Leave your rental car worries behind!