Please watch from 13:04 to 16:28 to know the real meaning behind 12 o clock. It has nothing to do with time as watches we have today were not invented back then. It refers to an old Indian game called chaupat, where one throws dice where 6 is the biggest number on each dice. When 6 appears on both dices, the total number is 12 and that is seen as sign of victory. Thus, each time Singhs rescued kidnapped Hindu girls, and would report back to their respective Jathedars stating "12 vajj gaye jee", which in fact meant we have achieved victory and have successfully rescued the innocent girls.
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥