If the wind did not abate or change, they would perforce have to wait another ten or twelve hours until the next tide, before a start could be made.

And the storm had not abated, the wind had not changed, and the tide was rapidly drawing out.
Marguerite felt the sickness of despair when she heard this melancholy news.

Only the most firm resolution kept her from totally breaking down, and thus adding to the young man's anxiety, which evidently had become very keen.
Though he tried to hide it, Marguerite could see that Sir Andrew was just as anxious as she was to reach his comrade and friend.

This enforced inactivity was terrible to them both.
How they spent that wearisome day at Dover, Marguerite could never afterwards say.

She was in terror of showing herself, lest Chauvelin's spies happened to be about, so she had a private sitting-room, and she and Sir Andrew sat there hour after hour, trying to take, at long intervals, some perfunctory meals, which little Sally would bring them, with nothing to do but to think, to conjecture, and only occasionally to hope.
The storm had abated just too late; the tide was by then too far out to allow a vessel to put off to sea.