Click the stop sign to start the project, and click the green flag to stop it. I just switched them around for fun ;)
So how DOES this work? Basically, there's a forever loop when the flag is clicked. Inside it, it has the "reset timer" block. This means the timer will always be at 0. But when you click the stop button, that script stops. So the timer starts running. There's a "when timer > 0.001" script that has all the code that happens when the stop button is clicked. The next bit is simple: When green flag clicked, stop all. Don't understand? Let me know in the comments and I'll try to explain clearer!