When you add a new machine to your account and Apple asks to validate it they charge $1 to your account to verify.
It remains on "hold" for the length of time your financial institution applies to holds, Apple has nothing to do with that. For most it's 3-7 days.
They don't "execute it and pull it back" they simply get an authorization code to determine if the card is valid then don't process the charge through. Helps to understand how banks handle $ transactions 🙂