LDSD doesn't really support empty date fields in quite this way, unlike the Classic product range (hint to LANDesk]
For better handling of dates
Instead you'll need to set the property of the attribute to enable checkboxes for the date (and possible the time). The idea is that if the check box isn't set, the date field is really empty (but it still visually displays the current date) Confusing I know, but hopefully not too much of an issue in training people to set/clear check boxes.
I'm not sure if there is a better alternative - does anyone else have some suggestions??