This mod supplies buildable clocks that tell the in-game time of day. There are two types of clock, both displaying a single hand on a 24-hour dial. (A 12-hour dial would be quite useless: the main use of a clock in Minetest is to check whether it's day or night, which is exactly what a 12-hour clock doesn't show.) One of the clocks moves the hand around a fixed dial, while the other moves the dial under a fixed hand. The latter is easier to read at a distance, because the two halves of the dial are easier to distinguish than the hand.
Currently the time is shown to the nearest hour. The clocks keep time by magic, as long as the map block they're in is being computed.
Available as public git repository, snapshot zip.