bittorrent etiquette question

[Gerhard Magnus]

I've been running azureus/bittorrent for about 4 hours and have
downloaded about 3/4 of the FC7 DVD iso.  As the incredibly cool "swarm"
panel of azureus informs me, I've also been helping a lot of other
people do the same thing.  My question is: what's the communal thing to
do after I've got my copy -- i.e. how long should I stay part of the
torrent in order to be doing what's considered fair? --Jerry