"Charging you" with a credit card is a two-step process. It works the way is does because of the restaurant environment.
First, they put through a "hold" on en estimated amount similar to what they expect the full amount to be. (Some credit card companies call these "Pending"charges.) This is what would be 'charged' at a restaurant, based on your bill plus a guess at the tip. Apple does the same. This estimated amount of your available credit is "set aside" so that you don't spend it on something else.
The money is not actually removed from your credit card account until the final transaction goes through. That can be minutes at a restaurant that reconciles instantly, hours if they wait until end-of-day, or days in the case of purchases from merchants.
The transaction to set aside tells Apple that at the time they checked, you are good for that payment, so they go ahead and build your computer. Most credit card companies require this 'pending + final' sequence to complete in under a few days. If not, the "pending" charge may expire on its own. When the final charge is ready, the merchant will charge you the full amount.
For Apple computer purchases, I think you will find this same timeline playing out for your credit card account. But if a week or more goes by, the 'set aside' would expire, and you could accidentally spend that money, leaving you without enough inside in your credit limit to pay for the computer when its final payment is due. You must manage your account to be sure you still have the credit limit available for that purchase -- Don't spend the money on something else!