The title refers to the time of day at which one of the kids at this fictional high school commits suicide. The movies grinds relentlessly towards this climax, which is depicted in graphic detail which won the film an R (ie 18+) rating from the censors. Meaning that the teenager audience it was aimed at would not be able to see it, as the censors didn't want to be responsible for any more of them topping themselves. (Fear not; they'll probably download it from the internet.)
It did have me thinking. I remember the attitude of the teachers at school that no problem was deadly serious if you were still alive the next day. It was inexplicable then but it feels natural now.
The cast is very youthful, mostly recruited straight out of acting school. Expect to see a lot more of them though.