If people have stuff to do then they are going, so a five minute ban won't matter.
IMHO, it should be ten minutes on the first time, so if you quit because you don't like the map or gametype or you think the opponents are too good, then you end up waiting just as long for the next game anyway. I don't have any sympathy for quitters, they simply leave the rest of the team to be spawn camped and are a major contributor to poor online games.