Clock modules are pretty much all the same, a control crystal provides the timing pulses, the coil is energised in one direction and then the other, which causes the magnet on the bottom of the smallest gear to rotate, half a turn per second and appropriate gearing from that point onwards to make all the hands rotate correctly. Simply cutting half the teeth off this smallest gear means that it will only turn the onwards gears half the time and the big hand will now take 24 hours to perform a single rotation.
The vague clock came about because people have different names for different parts of the day. Some people view afternoon as 12pm onwards (which it is) but when does midday start and end? So I decided to jot these all down and put them on the one clock face.
It's a hack, I'm worried about how well it will keep time but it seems to be ok at the moment. There are all sorts of other ways to change the tick length on a clock from changing the crystal oscillator, adding a frequency divider to the coil pulses, to full blown arduino with real time clock control that might work better.
This and all my other projects can be found on my blog at msraynsford.co.uk