It took 21 days for the $350 to leave my card... (mastercard)
As said at the start, I couldn't see the point of such a large hold on my card given I had pre-paid for everything, fuel, ldw/lis, etc etc etc....
Doesn't serve a purpose to hold that amount for fully prepaid!
Alamo got it right, they do $1 AUTH on fully pre-paid rentals, regardless of card used.