The initial sign up screen is set to be only visible when a column, let’s say, the “ProfileDone” does not equal 1. Then you have a button at the bottom of that screen that sets to increase the ProfileDone column by 1 when users have filled out all the required details. All other tabs are set to show only when ProfileDone equals 1, including the “User profile” tab.
Then in the User profile tab, filter email is signed in user, add an edit option and let a current timestamp value write to your revision column. Every time a user completes an edit that column will be updated.