In a true pace line you should rotate up and take a turn at pull. Your turn should end if you get tired or if you've been at the front for the length of time that club deems as a maximum. E.g. One of the clubs I ride with has a 2 mile max. It's OK to come off earlier if you're tired and can't keep the pace, but once you hit 2 miles, they want you to come off so that others can take a turn. We usually have enough strong riders that not everyone has to take a turn so the struggling riders can ride on the back no problem.

Another club I ride with has no max distance. It gets real annoying when we get someone on the front who won't give it up. I don't care how strong they are, that's not the point. Others want to take a turn.