1. Do the first level normally
2. After you press play on the first level, take a forward block and drag it in front of the first forward block in the solution. Without releasing the mouse, wait until the cursor indicates that it is not holding anything, and then you can release it.

Now, when you press the play on level 2, nothing happens. This is because from this point forward, each level uses the solution that was put in the previous level. The only way to complete level 2 now is to skip to level 3, input the solution to level 2, and then go back to level 2 and press the play button. After you press play, you are going to input the solution to level 3, and on level 3, you input the solution to level 4, and so on.

This glitch saves time because you now have the entire previous level to input your solution as long as you want, without losing any time at all. This allows for faster solutions, although they require more blocks to create them. The strats that I use for levels 5 and 6 are where I save most of my time, but they may not be perfect.

Have fun.