Why won’t turbo let me file my direct withdrawal payment date at 04/17/2018

Because today is the 17th and it's just not going to happen that fast.

You can either leave the date blank, or set the date for 4/18/18. The IRS has extended the date to pay and file by one day, so it will still be on time if dated for tomorrow.
For more information please refer to the article I am including below.

https://www.irs.gov/newsroom/irs-provides-additional-day-to-file-and-pay-for-taxpayers-through-wedne...