DW and Grandma Thora ring in the New Year at 12:00, and they wake up Arthur. Arthur looks at the clock less than 20 seconds afterwards, yet the clock already says 12:05.
The final scene shows animations from previous episodes. One of them is from "Sue Ellen Moves In" whose storyline should be set during the start of second semester in mid-late January or early February, but this episode is set during New Year's Eve (December 31).