How do you beat level 18 on johnny test tests of time

First jump down to the elevator. Then wait for 5-6 secs and jump 3-4 times. Then go to the time machine and use it. After that wait for the past Johnny to jump on to the elevator. As soon as he does this jump on to the button which activates the elevator. So now the past Johnny will take the missing piece by touching the laser which will make a box drop near the current Johnny. Then use the box to reach the time machine.