this happened to us too---I think they get so OT they get wired on adrenalin.
there was one nght where my son fell asleep for 25min and 7:35--woke at 8 and was totally content, aargh, no crying so I couldn't really use p/s. honeslty I left him in his crib---at least it was dark there and he got the picture it was bedtime. well he stayed in there happy for 2hrs---didn't start crying til 10pm. that was one of the nights where he only got 7hrs or so.
hugs..it does get better but you do have to be consistant.
that being said, if you do have to use a prop-make sure you do something other then the old way (ie holding or bf to sleep) swing, car ride is better.