Yeah shadrack, it could be anytime between 56 and 70...might even be a bit longer than 70, but I doubt it.
As far as when to start flushing...a good rule of thumb is to wait till you see all cloudy trichs with just a few going amber--if ya want it to be more couchlock. If more of a "heady"-high is what your after, then start your flush before they are all cloudy. That's just a rule of thumb though. You'll have to experiment a little to see what harvest time you like best according to the trichs.