They way a geyser works is when the super heated water overcomes the denser colder water on top with an explosive force. A slight constriction helps bisect the super hot and colder water. Changes in the container of that water can have effects on when this explosion happens or if it even does.

With this design I have chosen 6 such pipes that will each heat up water to go off on a different hour. Each pipe will only have to go off 4 times in a day.

Instead of a minute hand, I have decided that the pipes will be coated with liquid crystal around the area at the top where the water is cooler. This way a color change will be used to indicate what part of the hour we are into. Finally, the pipes will be numbered (possibly also in liquid crystal paint) to keep people from being confused.

These structures could also be built into the ground and take advantage of the natural thermal energy in areas where that energy is abundant. One can vary the length and the inside diameter of the pipe to get other time intervals.