On level 3 with Lisa you will do the Clueless mission. When you meet Milhouse at the docks, he will tell you to drive to the Springfield sign. Before you talk to him, drive your car north of Milhouse to the Itchy Scratchy shop. Then, go talk to him. When he is done talking, they will tell you to ''Get in your vehicle''. Run to the Itchy Scratchy shop and get into your vehicle. The timer will start and you will have more time.

When given a timed task, the timer will not start until you get in the car. Try the level on foot and the timer should not start.