Not sure, But some sources says that during Mughal period when sikhs were low in Number they used to attack Mughal army usually at midNight and vanish in the darkness , so term Bara baje is associated with those days

During the rule of mughal emperor Aurangzeb,,his soldiers used to pick wives and daughters of Hindus and sikhs so as to enslave them in the mughul Herem. These soldiers used to pick these girls and ladies from various parts of the cities and used to assemble at one location called as their transit camp. Sikh Forces who were soldiers of Guru Shri Gobind Singh used to attack these Mughal soldiers at 12.00 Noon when these captured ladies and girls used to be on way while being transported by moghul soldiers and at 12.00 night at the mughul soldiers transit camp it self thus freeing these captured ladies and girls of our community.

12 o'clock