[Musicians] Contra medley length?

I'm curious about other musicians' experiences with contra medleys, especially in relation to their length. I've played for quite a few 6x6 medleys (6 dances, done 6x each) and consider this a manageable length in a 4-person band (piano + 3 melody players), provided I remember not to play the entire time. Do any of you have experience with longer medleys? Have you played one that goes 30 minutes or longer? If so, how many musicians were in your group? What are your personal limits? Any experience alternating bands (or alternating individual musicians) in longer medleys? Thanks, Susie Lorand (fiddler), Ann Arbor, MI