Actually, the Janes book info has been pretty helpful.
And, considering the designers involved, I'm betting that the hexes are roughly 30 meters or 100 feet, and the turn lengths are roughly 10 seconds or so.

I've looked at the stats of some of the starter ships, and figuring out what a knot is, it's really hard to get a minute or anything larger with the dimensions of the ships involved and the amount of space they take up on the board.
Now! If they had gone to each ship occupying its own hex, then you'd be free to assume anything you want. But, they didn't.