Time in Delhi

India stretches from about 68° to 97° east, almost two hours of solar time, yet keeps one clock. IST is defined on the 82.5° east meridian, which passes near Mirzapur in Uttar Pradesh, and is maintained in New Delhi by the CSIR–National Physical Laboratory with atomic clocks. Delhi itself is at 77.2° east, so solar noon comes around 12:05 to 12:35 PM.

The single zone costs the northeast dearly: in Assam and Arunachal Pradesh the sun can rise before 4:30 AM in summer and set before 5:00 PM in winter. Tea estates in Assam have long kept an informal garden time, known as chai bagan time, about an hour ahead of IST to make use of the early light. Proposals for a second national zone have been studied, including by the National Physical Laboratory in 2018, but none has been adopted.

At 28.6° north, Delhi has a wider seasonal swing than Mumbai. Near the June solstice the sun rises around 5:25 AM and sets about 7:20 PM, almost 14 hours of daylight. In December sunrise is close to 7:10 AM and sunset about 5:30 PM, roughly 10 hours 20 minutes. Winter fog in December and January often hides the sun for much of the morning.

Central government offices in Delhi generally work 9:00 AM to 5:30 PM on weekdays. London is four and a half hours behind during British Summer Time and five and a half in winter, so a 2:30 PM meeting in Delhi is 10:00 or 9:00 AM in London. New York is nine and a half or ten and a half hours behind, which leaves the Delhi evening as the overlap. The IST to GMT page shows each hour side by side.