My group rides typically see most riders doing pulls for anywhere from 1-5 minutes, then moving off. There are always a few stronger riders who will do longer pulls. I'm fine with it.
The length of pulls is usually longer when our group is bigger. With smaller groups with similar level riders, we can be more organized and sometimes will rotate faster to get an echelon going, where riders are only doing 5-10 second pulls and there's more of a constant rotation. With bigger groups there seems to be less organization which results in stronger riders staying on the front to push the pace, and weaker riders sitting on in the back and not pulling through.
We also sometimes ride 2-wide for longer stretches without rotating. In these situations, the two front riders will almost always do longer pulls, then come off together and drop back. I think there's a bit of peer pressure in this situation for the two riders to "stick it out" on the front longer and not be the first one to suggest dropping back, and also the pace is usually more relaxed/casual when we're riding 2-wide, so there's more socializing and less concern about pace and sharing the load.
Either way, I'm never going to complain if someone wants to take an extra long pull, as long as they're holding the pace. I'm also unlikely to ever pull a group ride for more than a few minutes, regardless of how long others are pulling.