Visual Mechanical Timer
Sometimes when we tell the kids that they still have ten minutes on the tablet/TV/Lego and point to the clock, we sometimes get a slightly puzzled look that goes with the "Yes."
Our solution was to shout of the time as every minute passes, but that just increases the anxiety levels. The visual, red display of the mechanical timer shows them exactly how much time is left, allowing them to manage easier.
When you set the timer, the remaining minutes are displayed in red and they can see the remaining time reduce as the read area gets smaller and smaller.