Nintex form not showing default date value in a field

Why don't we back up a little. Why are you using the Wait Until date is not 01/01/1900? What are you trying to accomplish? Perhaps there's a better way.

So I need a trigger for when the date field is completed with a date, so the WF then knows when to update another field.

As you can't have wait until the date field is not empty I decided to default the date to 01/01/1900 and wait for this date to change to something else to use as the trigger.

Ok, if I'm understanding this, you have a workflow that doesn't need to run at all UNTIL a date field is set with ANY value, correct?

If that's the case, I would suggest setting up the conditional start on create and modify to check that date field. That way, you don't need to use the Wait Until.

Since you're forcing the field to be set as 01/01/1900, I'm assuming you don't know that a blank date field is actually equal to 01/01/0001. This means that you don't need to set the date field to anything. Just leave it blank by default. Then, in those conditional starts, check to see if that date field is greater than 01/01/0001.

By putting this into place, your workflow will not run at all UNTIL that date field is greater than 01/01/0001, meaning anything other than blank.

Try that and let me know how it works for you. And if I'm not understanding your desired process, please include some print screens to help explain it.

yes - that worked. 

I did not know that empty was  01/01/0001. I was using 01/01/1900 in the same kind of way although for some reason this did not work.

Many thanks!