how to make one: 1st take a once, and a number block. Connect the once to the number, then grab 2 labels. one will say "time left:" and the other will be the time left. make the number in the number block say how much time the level has, then connect its out put to the vaule input of the label. next grab a timer block and another number block. connect timer's out put into that number in input and that number's output into the other number's + input. grab another once block (or use the same one we are already using) and connect it to the timer's start input.make sure the delay of the timer is 10 and turn on always repeat. so every second the timer will go down by 1 second. grab a filter and connect the number connected into the label to it and make sure it is "less than 1" OR "EQUAL TO 0" then the pass into an next level block that will restart the level when the time runs out.
you can also use this in any other way. just remove the next level block