As per the description, this must be done in Time Limit mode. To unlock this mode, you need to play both Arcade and Wave mode once, score doesn't matter. Choose easy in Time Limit mode. The game will start with only two minutes on the clock. To maximise your time, you need to use your time travel power. Rewind will stop the clock. The best plan of attack is to use fast forward () as often as you can, whilst remaining alive. Fast forward will not make the clock go any faster, but will allow you to get further into the level and gain valuable time power-ups.
Whenever your time travel time is getting towards 4 seconds, use it. If the time on the clock is running out, rewind. This may take a few attempts, but you'll eventually manage 2:40.