EXCLUSION OF TIMES ALREADY INSERTED IN THE DATA VALIDATION

Hello everyone!

I am attaching the file in question.

In the "proposed intentions" sheet, in column G there are the times of the days in column F.

As you can see in column G I have inserted a data validation which allows me to insert only the times present in the "calendar+intentions" sheet. I inserted this data validation by creating another sheet: "daily timetables", in which I inserted all the days of the year (from January 1st to December 31st) and, on the line of the day, with a formula, I obtained all the times of that day from the "calendar + intentions" sheet.

My problem now is:

WHEN I ENTER A NEW DAY IN THE TABLE OF THE "PROPOSED INTENTIONS" SHEET AND CHOOSE THE TIME PRESENT IN THE DATA VALIDATION DROP-DOWN MENU IN THE CELL OF COLUMN G, HOW DO I MAKE SURE THAT WHEN I HAVE ALREADY ENTERED THE SAME DAY AND THE SAME TIME EXCLUDE ME THAT CERTAIN TIME?
(For example, since I entered January 1st at 12:00, having generally 4 times available for that day (8:00 - 10:30 - 12:00 - 18:30), when I enter January 1 again, when I click on the time cell, it should return only the times 8:00 - 10:30 - 18:30, since the time 12:00 has already been entered).

To those who want to help me, I only ask not to use Macros and VBA as a solution.

Thank you,

Luciano