There is no float time for paying by direct debit. It sometimes takes a couple of days after you file for the IRS to actually make the withdrawal, but you can't count on that. Make sure the money is in your bank account before you e-file the tax return.
Your payment was due April 18, not October 16. The extension is an extension of time to file your tax return, not to pay the tax. The IRS will send you a bill for interest and penalties for late filing. TurboTax cannot calculate the interest and penalties.
