Manage "empty" Dates From DTPicker Control

I'm having a problem with a form where I have created several DatePicker controls.
Once the user select the control and select a date, it's saved on a cell (all the data is stored as a record, including dates). However, the user could not select a date, and, in this case, I should record nothing on that cell. What I have done is to enable the checkbox property.. so I assumed that the date is valid if this checkbox is checked (however, I don't know how to validate if this checkbox is checked or not). The checkbox property for the date picker is a yes/no value that just show the control as enabled/disabled whether you check or not that checkbox.

Question I have is: How can I do to see if I should be saving a date or not on the cell? I have tried different formulas without success. Sometime works and sometime no. I'm using the following code to validate if the user has selected a date:

If IsNull(DTPicker18.Value) = False Then
Worksheets("DAT").Cells(nPubRow, 37).Value = DTPicker18.Value
Else
' If the user deselected the checkbox I should delete the cell content...
Worksheets("DAT").Cells(nPubRow, 37).Delete
End If

What happens is that sometimes this condition returns True.. but others it returns a 0:0:00 value that is not null.