When creating Date Time properties, the Show None option is disabled by default.  This prevents you from placing or editing features with a null value for the date.

To overcome this, enable Show None which adds a toggle to the Date Time property.

If the tick box is on,  the date property is saved when placing new feature instances.  When the tick box is off, the date is not saved resulting in a null value.

NOTE:  The Data Browser does not recognize or support the Show None toggle.  For this reason, use the Edit Feature tool to make changes to date fields with the Show None option.

A OpenCities Map CONNECT Edition sample schema is attached for your learning.

communities.bentley.com/.../DateShowNone.zip

There is another instance when you may see a blank Date field after using the Place Feature tool - When the Initial Value field is set to None.  Placing a feature will show the DateTimeProperty correctly in the Place Feature dialog box, but after placing the feature the Analyze report shows the field empty.  Set the Type to dateRegionalShort and you will not have to pick the Date in the Place Feature dialog, it will remain in the Analyze report for all features placed.