The payment is made on the same day or at a future date which you can specify.
For example, on the day on which you receive your OTE bill, you can schedule its payment to be made on the final date for payment. You can also choose to block the payment amount (without any interest loss) in your account, in order to ensure that it will be available on the payment date.
Payment orders to be executed on the same day must be submitted by 22:00 at the latest.
Especially for payments to your credit cards, you may choose "immediate execution", in which case your available balance is adjusted at the moment of payment.