Google Ads will charge directly to your credit card after 30 days of serving ads or when you hit your monthly budgeting threshold. Most of the time, these two things happen at the same time, since daily budgets average out to equal the monthly budget, but variables can, on occasion, push the billing date backwards or forwards a day depending on the month in question.
Google will never exceed your monthly budget, though it may spend up to 2x your daily budget on any given day. It will always average that spend out on a slower day.