I want to use a time stamp to notify if a modification is made after a approval checkbox is checked

Should I fully understand your conundrum, but it seems to have to do with the fact that the very last update to the date update it is one you would rather not have.


A solution is to have the approval happening a child table to Float up the most recent approval status up to the parent record.

So the approve button but actually be a button that adds that child record.