About the lowering of the flag when the sun sets or not later than nine o'clock. That is a common wisdom in the Stockholm archipelago, which we all follow very strictly.
But I have a very good old friend who has tought me a lot about the art of sailing and he never lowered the flag. He insisted that a boat on the move always have the flag hoisted, even if you have a temporary stop in a overnight harbour. Here in the harbours of Bornholm, hardly anyone lower their flags, regardless if they are Danish, German, Dutch or Swedish boats. So perhaps my friend has a point here, and how is it with the visiting cruising ships in Stockholm, do they lower their national flags overnight in Stockholm.
Nevertheless, we keep our flag up now, at least when we are down here, far away from the Stockholm archipelago. It's very convenient.
PS. My very good old friend also had the flag hoisted during the winter season on dry land, that is perhaps to push it a bit too far. DS.