When setting up your account
Your service will start running almost immediately after you enter valid credit card information in your new Google billing account. However, in special circumstances, it can take a few hours.
When using the Make a Payment feature
When you use the Make a Payment feature, our system will authorize your card almost immediately for the amount of the charge. This means that our system checks with your credit card provider to ensure that your card has enough credit available to cover the charge.
If you're on automatic payments and your service stopped running due to a declined payment, it'll start running again after your payment is authorized.
It might take several more hours for the payment to appear on your Transaction history page (under the Billing tab).