You post doesn't make sense. You don't wait for anything. You need to pay the tax due as soon as soon as possible. You actually need to make an estimated payment when you file the extension by April 15. The IRS doesn't bill you and won't bill you for the interest until they get your return and tax due payment. The interest stops accumulating as soon as the IRS gets your tax due payment. Then they calculate the extra interest if any and bill you.
And even if you or Turbo Tax adds it on line 23 it is only an estimate. It's common and expected for the IRS to bill you for more depending on when they actually get your payment. Or even send you a refund for some.
