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If I understood you correctly you want to prevent your users to select same date.
You can achieve that with Date Reservation widget.
However Date Reservation does not have time option. If you want to have both date and time options, that I would suggest you to use Appointment Slots widget.
Inside of this guide you can find how to add widget to your form:
If I did not understood your question correctly, please explain in more details what you are trying to achieve.
Hope this will help. Let us know if you need further assistance.