You have until the deadline for filing the individual tax return -- April 18, 2017 -- to make a contribution to an IRA.
When you click on the Traditional and Roth IRA Contributions heading in TurboTax (Federal Taxes > Deductions & Credits > Retirement & Investments) you'll be asked Did you contribute to a Traditional IRA, and you'll see the special note telling you to answer "yes" if you plan to make a regular contribution by April 18, 2017.