If I initiated an EFT for an IRA TY2017 contribution on 4/13/18 and it completes after 4/17/18, what does the IRS consider as the Contribution Date?

Trying to avoid filing a return that indicates I have made a contribution to my IRA for TY2017 but the IRS will consider it for 2018 since the transaction didn't complete before midnight on the 17th.  

Not sure if this is treated like the postmark on a paper filed return (would be Apr 13) or not.