2x11 - Dexter's Laboratory

Dexter oversleeps and still has to finish his homework along with getting ready for school and eating breakfast, so he creates a helmet that expands thirty seconds into thirty minutes, but realizes that slowing down time is more detrimental than helpful. When he gets everything done, the helmet shuts off. But Dee Dee blocks his door causing him to miss the bus. When Dexter asks Dee Dee why, she replies "Snow Day, school's canceled!". Dexter realizes he did all that rushing around for nothing!