I don't know if there is a link between the longer routine and overstimulation. Ours can get up to an hour and he can be all jumping around and once you plop him in bed, he's gone cold. But then, all kids are different.
Re parent's party: we talk about the fact that we are sleepy too and that we need sleep. Sometimes I'm so tired towards the end of the routine that I'm yawning and need to tell him that he needs to sleep so that I can too. Maybe that would work for you?
