If you mailed a check, mailing time plus opening, moving to banking area, prepare and finally post the check. It could be a week from the time you mailed it, or more.
If you selected direct debit, the date you selected is the earliest the IRS can withdraw the money. It usually takes a few days after accepting your return for them to make the debit.
fanfare is right. If the IRS does a debit without enough money, the IRS won't be paid. You will need to pay your bill online instead.