I didn't say it HAD to be, just that once the sun goes down it seems bad things happen, so if your purpose of protesting is to protest and not throw bottles/loot/burn then go home when it gets dark. Even if it's only for one or two nights to let things calm down. Keep going out during the day by all means, just let things cool down.
This is what I'm trying to say, and it's not limited to this incident at all.
John 3:19..' and men loved darkness rather than light, because their deeds were evil. ' Been that way since way back.