World Cruising Club stand at the Boat Show had a short talk on navigating by the stars, and having fond memories of the night's sky mid Atlantic boosted by reading Tristan's book on Natural Navigation, I went along for a prep.
Most of it was based upon spotting Polaris but there was one nice trick about how to use it and the Plough to work out your time.
Basically look at the night's sky and think of a back to front clock as in the graphic above, and then work out the "sky hour" of the leading edge of the Plough.
Then the time can be estimated using:
Time = 41.5 - (2 * SkyHour + 2 * Month)
So if the sky hour is 7 at its April then the real time is:
Time = 41.5 - (14 + 8) = 19.5 = 7.30 pm
More detail in "The Natural Navigator" footnotes for the chapter on The Firmament.