"I don't like Mondays"

The Boomtown Rats recorded a memorable song about one of the early famed school shooters (I assume there have always been such, but one of the first in the modern media era), a girl who it was reported told police her reason was "I don't like Mondays."

Question: Are these planned mass-shooting things often on Mondays? It makes sense—someone makes preparations over the week-end and, having decided to act, there's no reason to wait.

(I assume this would be different from other, more directed, school violence which would be liklier to follow something happening at school. Someone does something to someone on Tuesday who then brings a gun to school on Wednesday, etc.)