"Three o'clock sharp this afternoon, you die."

[MikeNUFC]

"The plot concerns a student (Casey Siemaszko) who accidentally offends a bully (Richard Tyson) and who devotes most of his school day to avoiding a fistfight with the bully at 3:00 p.m"

I don't think it's much of a reach to be honest. Em's always been strongly into films.

[_Hawk_]

Anyone seen Slumdog Milionaire? It's common for your brain to absorb everything you see during your lifetime, but to only allow you access to certain memories which are relevant, or noteworthy. The rest orbits your subconscious. Thus Em might have witnessed this film sometime during his life (whether in the cinema or when it was advertised) and so when he wrote the rhyme, the time school finished connected with his stored memory of the film.

[Solace]

I like this movie.

[Solace]

For me, my elementary finished at 3:30, my junior high finished at 3:00, and my high school right now finishes at 3:15. I've always been under the assumptions it's around the same for everyone.