Before one could know another, i.e. while it was yet so dark that one person could not discern another. Or, before one did know the other, i.e. before they were carnally known to one another. Let it not be known that a woman came into the floor; he takes care to preserve not only his conscience towards God, but his reputation, and hers also, among men.
Related Commentaries of Ruth 3:14
Ruth 3:14
14 And she lay at his feet until the morning: and she rose up before one could know another. And he said, Let it not be known that a woman came into the floor.