As one who used to work the Front Desk at a Hilton family property:

The debit card will be "charged" immediately when you check in, for the amount of the stay AND up to $100/day of your stay. That amount of money will be totally unavailable to you during your stay and some time after. When you check out, it can take up 14 days to get the money back to your account (it depends on the financial institution, not the hotel).

I had a honeymoon couple check in on a Saturday - gave me their debit card for their 5 night stay. When they went out to dinner that night, they discovered their card was refused at the restaurant. Poor kids had NO money left on the account!!! The only place they could eat was at the hotel, where they put the bills on their folio. They couldn't go shopping or do anything that cost. They had to get one of their parents to deposit more money in their account after the weekend...

What I always recommend after that: If you have a credit card, use it for the reservation (unless a pre-pay) guarantee and when you check in. It only does an authorization, not an actual charge at that time. When you want to pay, feel free to change over to the debit card for the actual payment. The authorizations will fall off your CC and no charges occurred.