Drama, Drama ! !
The yard I have been using for the past 6-7 years closes by mid afternoon on Saturdays and resumes work on Mon morning.For many years now, I have been having them haul my boat as their last boat out on Saturday, and purposefully leave it in the slings till Mon morning so that I can paint the bottom. Two advantages to leaving it in the slings, less cost because they aren't blocking it, and more importantly, I can paint the underside of the keel (and rudder) really well; not just 1 quick coat just before putting it back in the water ( which probably doesn't "stick", because most paints require 12+hrs to set up properly). I feel that the unpainted area under the straps (which can be painted every other hauling) is less of an issue than the underside of the keel. But that's just my preference.As far as how long a boat could be left in the slings without damage; Robert's post may be correct. I'd be interested to know how marine engineers might answer the question.