Meanwhile, I did notice a bug - or at least what may be a bug, unless this was the intent: Reboot/restart of the status menu doesn't save the clock you have selected before. So no matter what you select the next hildon-menu restart (reboots included obviously) sets it back to Decimal.
Also, I started experimenting through trial and error, and made my own clock ("Test Clock" - for obvious reasons). Nothing exciting yet, but I should be able to start making possibly useful clock styles soon.