My 2018 has been accepted by the IRS. How come the amount I owe hasn’t been taken from my checking account on file? How do I ensure it will be paid by the deadline?

We can't help you with that because all we do is transmit your requested method of payment to the IRS and state.  Only they can initiate a transaction and they don't tell us when they do.  You can ask your bank if there's a pending withdrawal.