I have picked up early with
Alamo & kiosk. (I always make my pickup time about 1 hr. after flight arrival time just in case of delays, baggage issues, etc. so I don't lose my rental car. Same with extra late drop off time in case of flat tire, etc. )
Anyway, the kiosk knows that you're early and it will ask you if you agree to the added charges, I think an extra hourly charge was around $10 for a midsize SUV. It doesn't actually charge you the extra $$ if your return time results in the same time period that you originally booked. I agree to the charges but usually drop off a bit early too so it works out to the same # of days rented.
So if you're scheduled for 11 am pick up
and 11 am drop off, and you pick up at 10am, you will now have it for more than 24 hrs, resulting in an extra charge.
If you have 11am pick up and 6 pm drop off, it wouldn't change anything, as you're already paying for another day. kwim?
I hope I'm making sense, I'm a little sleep deprived.
