Thanks. I can reproduce the time bug. It's weird. If I narrow down when it stops working, I get that time passes on May 7th, but not May 8th. Perhaps it's something to do with numerical precision - maybe I'm using integer time inappropriately somewhere.
On the sails - I tried this a few times, and didn't see any consistent pattern. It should depend on the force of the wind (so more for topsails) times some factor varying with the size of the sail, and some randomization. (I've upgraded my system recently and haven't installed unity yet, so it's difficult to check some of this.)
Stability, I'm afraid, is something that is not modelled well. I didn't think about it until rather late, after I had the buoyancy and hydrodynamics tuned for the simplified hull form I was using. When I realized it was too unstable/stable (I don't remember), I tried a simple fix by moving the centre of gravity up and down when the ship heels, until the behaviour seemed plausible (I did look at some stability diagrams).