If the project you’re backing is successfully funded, your card will be charged when the project reaches its funding deadline. If the project does not reach its funding goal, your card is never charged.
If you've backed a project that is still live and are seeing a charge on your bank statement, what you are likely seeing is a temporary authorization of funds. The time it takes for an authorization to clear varies on the bank, but typically takes 1 - 3 days. You will not be charged until the project you backed has ended successfully.