When I was painting the hull I noticed that if I went over the first light coat of Killrust (which was applied over two undercoats) after about five minutes the second coat covered very well, though it did appear to be a little thick. This was confirmed 24 hours later as it showed bad runs.
After three days the thicker paint, though skinned, wasn't actually dry under the skin. I've rubbed the whole hull down with sandpaper, which removed the skin and exposed the wet paint underneath. I'll wait a couple of days for this to dry and hopefully be able to re-coat.
From now on it's one thin coat, light sand, second coat. Just like the instructions say!