Another side effect generated from the experience : There is no time limit for flipping the first coin, so if the guard choses the first square, I would wait 1

Another side effect generated from the experience : There is no time limit for flipping the first coin, so if the guard choses the first square, I would wait 1 min before flipping mine. 60th square ? I would wait an hour. If my friend outside is able to know precisely when I enter / exit from the room, he is able to know the correct square.