If your client wants to pay on Oct 15th, you could hold the return and file on that date. The funds will be withdrawn within about 2 business days.
ATX has the same issue as Drake, you can't go out even 1 day. I filed a return a few weeks ago after the end of the banking day, so smart me I put in the next day as the bank withdrawal date. REJECTED. Even at 10PM. It is just the rule that if you owe and you efile and you want the direct debit option you pay immediately...but I don't have a source for that rule.
Tom
Longview, TX