Mumbai

All of India keeps one clock, India Standard Time (UTC+5:30), measured from the 82.5° East meridian near Mirzapur in Uttar Pradesh. Mumbai sits at about 72.9° East — nearly ten degrees west of that line — so the sun rises and sets about 38 minutes later than it would on the reference meridian. That is why winter sunrises in Mumbai come after 7 a.m., while summer sunsets are close to 7:20 p.m.

Mumbai held on to its own time longer than any other Indian city. "Bombay Time", about 4 hours 51 minutes ahead of Greenwich, was used locally from the late 19th century, and the city kept it even after IST was introduced in 1906, only switching fully to IST in 1955.

India spans about 30 degrees of longitude, so the single time zone is a compromise. In the north-east the sun can rise nearly two hours earlier than in Gujarat, and tea gardens in Assam traditionally ran on their own "chaibagan time", one hour ahead of IST. Proposals for a second time zone are studied from time to time but have not been adopted.

For business, the NSE and BSE trade from 9:15 a.m. to 3:30 p.m. IST, overlapping with the Asian afternoon and the European morning. The half-hour offset means meeting slots often land on the half hour — 2:30 p.m. in Mumbai is 9:00 a.m. in London in winter. Major festivals such as Ganesh Chaturthi and Diwali follow the Hindu lunisolar calendar, so their dates move each year between August and November.