It is useless if you can't even control yourself, You would set an alarm and tell yourself that you would stop after it rings but you are already losing or winning and you are being greedy to play more to win more or win back what you lose so the alarm would just be useless.
Really useless if a gambling casinos has this feature but you refuse to be aware of it, when it comes to limitation in gambling it should be the concern of the gambler or get someone you trust that will stop you when you are going over time and losing money that is over your budget, we cannot get a gambling site to automatically do this for you.