Good Morning Farooq.
Researching for this question shows me that this is not possible.
Managing and/or creating variables in SC/Admin/Report Builder/Data Object, does not show any possibility to remove the time section from the 'date'-type variable.
The next proposal then is to open an Idea in this same community.
To see whether it would be possible to implement such in a future release of the product.
Thanks and kind regards, Louis van Amelsfort.