I am happy to share my paper titled Introduction of The Indian Standard Time – A Historical Survey that traces the history of Indian Standard Time (IST) based on hitherto largely unpublished original documents from National Archives and elsewhere.
In ancient India time was measured in units called ghaṭīs by means of the sinking bowl type of water clock. In the late fourteenth century, Firoze Shah Tugluq adopted this water clock and the time units, so did Mughal rulers from Babur onwards. This custom was emulated also by East India Company at its factories in the seventeenth century. In the second half of the nineteenth century, the British Crown assumed direct control of the subcontinent, and began to replace the water clocks progressively by mechanical clocks. However, every locality followed its local time. In 1905 this plethora of local times were abandoned in favour of standard time 5 ½ hours ahead of the Greenwich Mean Time (GMT).
The paper is available on Academia https://www.academia.edu/45449585/INTRODUCTION_OF_THE_INDIAN_STANDARD_TIME_A_HISTORICAL_SURVEY
In the paper, I discuss – How was time measured in ancient India? How was it adapted by Firoze Shah Tughluq and later by the Mughals? When and how was the mechanical clock introduced in India? How did the British arrive at the conclusion to implement a standard time and how was it approved by Lord Curzon? Till when did Bombay and Calcutta retain their local times even after the Independence? Does it now make sense to introduce multiple time zones in India?