I am implementing search functionality in WinForms and I search by date range. Thus there are dateForm and dateTo date pickers on the form. By default their values are date
You can set DateDateTimePicker.Format property to Custom.
DateDateTimePicker.Format
Custom
Then set DateDateTimePicker.CustomFormat property to your default text (e.g "N/A" or a space " ")
DateDateTimePicker.CustomFormat
"N/A"
" "
After the user has selected a certain date value, you should set back the format property to short etc.
Hope this helps!