Hi there GroGreen,
The Control should expect a format similar to the following (Either should work, and the control will figure out the conversion if the Display Format is different from what is entered)
May-29-2017 10:27 AM - Short Date and Time
Mon, May 29, 2017 10:28 AM - Long Date and Time
However - it appears there is a problem with the control accepting Manually set Date/Times at the moment. I've brought this one up with the team, and we will look into a fix for this one.
In the Meantime, It seems that Actions which update this control still work correctly - so a potential workaround would be to have an Update Controls on Screen action set On Screen Focus Which Updates your Date/Time Picker with a date following one of the above formats.
Thanks GroGreen!
-Ben