I have used the timers when my kids went through this for warnings or timeouts. I used the oven timer, microwave timer or my phone. " in 5 minutes when the timer goes beep, it's time to ____" "2 minutes of time out, timeout is over when the timer goes beep" it worked great and I eventually I didn't have to use it anymore. I'm also quite strict and I don't tolerate that kind of behavior. I find ignoring it works well when it's only 1 child, make sure they are safe and walk away. But when in a group / daycare setting I don't believe it's the best way to do it as its not that easy to just walk away. I also think it's important to show them and other kids that it is NOT an acceptable behavior.