Grace periods for credit cards
Grace periods for credit cards refer to the period between when you acquire the debt and interest starts accruing. It's typically about 21 days but can be as many as 25 days. It would be a rare thing to find a credit card offering anything beyond that. So, if you charge $300 on your credit card, you'd have 21 days to pay that balance in full without any interest accruing.
However, there's a catch to all of this. If you're carrying a balance, you may not have a grace period at all. For many credit cards, that's the deal. You get a grace period if you pay in full every month (or have paid your balance off entirely for a while before you use it again), but if you don't use your card in that way, you don't. Check your cardholder agreement for the exact terms of your grace period.