Date and Time Picker Problems, Can I make the cell blank?

Hi, am using a Date and Time Picker as I have in a few of the cells in Column B of my sample worksheet, which asks the user of this training spreadsheet to enter a date. To simplify it for the users, I inserted what I think is a Date and Time Picker (its in cells B7:B14). I like everything about it EXCEPT the fact that the cell cannot be left blank until a date is selected. So if the user of this spreadsheet wants to, they can leave the drop-down box, or picker blank before they select a date. Is there a way to do this?

Or, is there another way to enter a date in the cell using a calendar similar to the date and time picker. I would like this option to be in all the cells in column B where there is an adjacent "work instruction" in Column B. Anyone?