I do remember a story teller at one Getaway whose story, although amusing, went on for at least 20 minutes. This was at a sing-a-round and people left to go sing.
Though I would love to hear about Uriah's birthday streak complete with the Dunbar Sisters' milkman and cat, I agree that a five minute limit is fair. One of the joys of these workshops is to see someone who never sang or told a tale before jump in and "perform". And it is frustrating to prepare a piece and never have a chance to do it because someone else chose a 50 stanza ballad or a reading of the US Constitution.