Although your suggestion is Wright, but sometimes our emotions plays a big role in our lives. If you can't control your emotion you can't control your time. Because when ever your emotion I'd working time has nothing to do. Although the time and emotion works together but I think it's your emotion that control the time because there will be a point in time when you loss more often and you choose to continue until you win without considering the time countdown and it will definitely affect you.
But putting a timer might help us than not putting at all. This is because when we see the timer, we can pause for a while and think if we are committed on changing our selves for the better. If yes, then we will decide to stop no matter how hard it is or even if the urge is still there. If time is not important, there won't also be clocks around that will be invented.
Don't you think that putting such timer might make you to over leverage because you want to beat the time? With such timer, you will increase the factors of consideration in your decision making and the more the factors, the poorer the outcome will be. To me I don't see the method of adding timer ideal because it will only agitate the gambler and not add anything positive.
Before getting started with gambling, it is best to make plans on everything that might possibly happen in the gambling process. Some good gamblers go as far as determining the risk and profit target before they start. I think this will be a better guide than the timer.