Probably today. I see no reason for putting a bomb in a mail box and blowing it all to hell. Sure it happened to be on the road away from the house so no houses were damaged but the shrapnel could have got any car going by, and could have done house damage. Also it happens to be a federal crime.
Sure it is fun to play with bombs and blow stuff up but you don't blow up other peoples property and you don't do it where there is that great of a chance of personal injury from flying mailbox fragments.
When was the last time you ate ice cream?