In 78 CE, the Hindu king Vikramaditya defeated him and killed him in the Karur region, located between Multan and the castle of Loni. The astronomers and other people started using this date as the beginning of a new era.’
As the empire of Bharatvarsha functioned from the present India( read Vikramadityas World Empire),the world seems to have followed the Indian day concept,that is beginning in the morning.
That is taking 5.30 am as the Sun rises in India,12 midnight has been taken as the beginning of a new day.
One must remember that Britain was ruling the world,colonising the countries.