October 30th
October 30th
[A kid dressed up in a lab coat and goggles is standing on a neighbor's doorstep.] Kid: Trick or treat! Neighbor: Nice Doc Brown costume, but today's October 30th. Kid: Great Scott, I must have overshot!

For Halloween, a child has dressed up as Dr. Emmett L. Brown (played by Christopher Lloyd ) from the Back to the Future film trilogy. In the films, Brown created a time machine out of a DeLorean DMC-12 car, which he and teenage protagonist Marty McFly use to travel through time.
The joke of the comic is that Halloween is on October 31st, and by showing up dressed as Doc Brown on October 30th, the kid can make the joke that he "overshot" the time machine and went back one more day than he meant to. Doc is heard throughout the movie franchise saying "Great Scott" as an exclamation of surprise.
The title text suggests an inventive use of time-travel to get ten times the candy — hitting each house at a 30-year interval up until 2300. The interval matches that of the first two BttF movies, which take place in the years 1955, 1985 (the present at the time), and 2015.
Of course, one would have no idea starting off if Halloween is still being celebrated in 2300, or indeed if the human race even still exists.
[A kid dressed up in a lab coat and goggles is standing on a neighbor's doorstep.] Kid: Trick or treat! Neighbor: Nice Doc Brown costume, but today's October 30th. Kid: Great Scott, I must have overshot!
