@marcyvq: Yakou said during the beginning of the gamble that he would try reviving the person who is in the "near-death" state, but not indefinitely. Rather he would only spend a limited time (15 chest compressions, which he said would take ~10 seconds) before stopping. Check out chapter 492 pages 11 and 12 for that info.
@marcyvq: Yeah, that is a stopwatch and Yakou has been using it to time how many seconds pass once the handkerchief hits the ground until the Checker turns his head.