navyfield, you have no cllue what your talking about. That three seconds allows everything to stop moving, letting you FINISH THE LEVEL. And with Trebuchets, the power bar would mean nothing. They are designed tot ake avdantage of different angles and not power.
For level 20, soften the fall of the box. have it hang from the bottom hinges of the top part, and use the other hinges for reinforcment. You don't need to use steel.