I have no problem with having my seatbelt loosely fasted during the entire flight.
While the security risk might be considered minimal after the a/c has come to a complete stop, I usually open my seat belt only after the engines have been shut down. I make that sometimes even deliberately in order to slow all those people down, that choose to have the window-seat, but on the other hand cannot await to get off board and try to get out of the seat row, while the a/c barely has stopped.
I recall having read an article quite a number of years ago about airline-service by Aeroflot within the Soviet Union: There it was mentioned, that most frequent-flying pax, sat in their seats (presumably with their seatbelts fastened) until the cockpit-crew emerged from theit cockpit ! Pax considered it unsafe to stand up, as it was not gueanteed, that the a/c has reached its final destination yet (read: not continue to "taxi" but "taking to the skies" again".
For the exact time the "Fasten seat belt"-sign is switched off, to my experience it most times is done after power has been cut to the engines.
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !