This is the time of day when one has retired to their place of sleep, to end a tiresome day. When suddenly, they are awoken by a mind boggling thought they had earlier that day. The time when awoken, would be referred to as 'stupid o'clock'.
Michael: " oh no , i forgot what my homework was. I didn't write detailed enough note in my folder."
Stephanie: "you'll think of it at like Stupid O'clock tonight"