A failed UPI payment between two banks can be reconciled only if both banks' servers agree on when it was attempted. An investigator trying to reconstruct the order of trades in a market-manipulation case needs to know, to the microsecond, which order was placed first. A grid operator working out why a substation tripped depends on time-stamped fault records. For each of these tasks, there needs to be a mechanism that we all take for granted today: that every clock involved in the world is telling the same time, to the millisecond or better.
Today, that mechanism is mostly an approximation. India's banks, exchanges, telecom networks, power grids and data centres draw time from a mix of sources — the CSIR-National Physical Laboratory in Delhi, GPS satellites operated by the US government, and public internet time servers, some hosted abroad.
But that changes from early 2027: the government on Monday announced it has notified the Legal Metrology (Indian Standard Time) Rules, 2026, under which every clock used for legal, administrative, commercial or official purposes must trace back to Indian Standard Time as maintained by an Indian institution. Using any other source will be a violation of law.
How India keeps time
Indian Standard Time is generated at the CSIR-National Physical Laboratory in Delhi, the country's designated national metrology institute and its official timekeeper. The laboratory relies on an ensemble of atomic clocks — caesium clocks and hydrogen masers, according to CSIR-NPL — and averages their readings to produce a single national timescale. That timescale is held to within a few nanoseconds of the international reference maintained in Paris, against which every country's official time is measured.
{{/usCountry}}Indian Standard Time is generated at the CSIR-National Physical Laboratory in Delhi, the country's designated national metrology institute and its official timekeeper. The laboratory relies on an ensemble of atomic clocks — caesium clocks and hydrogen masers, according to CSIR-NPL — and averages their readings to produce a single national timescale. That timescale is held to within a few nanoseconds of the international reference maintained in Paris, against which every country's official time is measured.
{{/usCountry}}Why atomic clock to synchronise time? An atomic clock keeps time by counting oscillations of caesium atoms, a physical constant that does not drift the way a quartz wristwatch does. Several clocks are run together so that a fault, drift or failure in any one does not shift the national time.
The more difficult problem is delivery. Generating accurate time in a Delhi laboratory is straightforward. Getting it, unaltered and on demand, to a bank's data centre in Mumbai, a substation in Guwahati or a stock exchange server in Chennai is where the engineering lies, and that is where the new rules lay down some specifications.
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The delivery
The Department of Consumer Affairs, working with CSIR-NPL and the Indian Space Research Organisation (Isro), is setting up five Regional Reference Standard Laboratories — at Ahmedabad, Bengaluru, Bhubaneswar, Faridabad and Guwahati — to act as regional relay points for IST-traceable time.
In July, the minister for consumer affairs commissioned a White Rabbit-based dissemination network at RRSL Bengaluru. White Rabbit is a fibre-optic timing protocol that lets two clocks in different cities stay synchronised to better than a billionth of a second. The network has already been used to send IST securely from Bengaluru to the National Stock Exchange’s Chennai facility, with CSIR-NPL, ISRO, SEBI, NSE and BSNL as partners, according to the ministry.
Unravelling from GPS
The rules also formally admit NavIC, India's satellite navigation system, as an approved timing source. Every NavIC satellite carries an atomic clock synchronised to IST at CSIR-NPL, giving the country an over-the-air time signal that does not depend on a foreign satellite constellation.
The ministry has said, “At present, several systems use foreign satellite-based time sources. The development of an Indian time dissemination infrastructure will provide additional options for critical systems and reduce dependence on external time sources.” The same concern has driven every country with a serious critical-infrastructure base to build its own timing sovereignty.
The “foreign satellite-based time sources” the ministry refers to are, in practice, GPS — a constellation operated by the US government and, since 2019, by the United States Space Force. Indian civilian users, from truck fleets to smartphone owners, have had reliable, free access to GPS timing for decades, and the ministry has not proposed cutting them off from it.
What the rules do is require regulated entities to derive their operational time from Indian sources, so that no critical system in the country runs entirely on a signal whose operating parameters lie outside Indian jurisdiction. The direction has been building for years. The Indian Computer Emergency Response Team, in an April 2022 directive, already required entities running critical information infrastructure to synchronise their clocks with time servers maintained by the National Informatics Centre or CSIR-NPL, or with servers traceable to them. The 2026 rules extend that principle beyond ICT infrastructure to every regulated sector, and give it legal force.
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Who has to change what, and by when
The rules come into force 180 days after gazette publication, according to the ministry, which puts commencement in early 2027.
Government departments and public institutions will have to display IST on all time-keeping devices and synchronise them via standard network protocols, using an approved Indian source. Regulated entities in banking, capital markets, telecom and power will have to re-point their time synchronisation away from foreign servers and bare GPS receivers, towards IST-traceable sources — through NPL’s network servers today, and progressively through NavIC and the White Rabbit fibre network as those become available.
The precise numeric accuracy tolerance a bank or an exchange will have to hold on to remains unfixed. The ministry has said accuracy standards will be issued as advisories.
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What to watch
The compliance advisories that will set operational tolerances by sectors have yet to be issued. Watch for them from the Department of Consumer Affairs, in coordination with the Reserve Bank of India, SEBI, Trai, the ministry of power and the railways.
The build-out of the remaining four RRSL secondary timing centres, beyond the one at Bengaluru, is the physical prerequisite for nationwide compliance. Progress on those centres will decide how binding the 180-day runway proves in practice.