How India’s new IST rules aim to put the country on one clock

On August 27, the Union Consumer Affairs Ministry notified new rules making Indian Standard Time (IST) legally enforceable for official and commercial use. These Legal Metrology (Indian Standard Time) Rules, 2026 require time-dependent systems in government and critical sectors to use a traceable, authorized IST reference, with a 180-day compliance period.

While India has historically followed IST, the new rules were needed to improve time coordination and enhance cybersecurity, reduce crime, and make critical infrastructure more resilient.

The Department of Legal Metrology, responsible for enforcing measurements like mass and volume, needed an equivalent capability for time. Until now, there was no legal status for time, making it difficult to compare events or measurements. The new rules aim to give time a legal status, comparable to physical measurements, and make IST the country's common legal time reference.

The Council of Scientific and Industrial Research's National Physical Laboratory (CSIR-NPL) maintains IST by operating extremely precise atomic clocks. IST is UTC (NPLI) plus five hours and 30 minutes. Time is disseminated through various methods, with the most common being the Network Time Protocol (NTP) server. However, this default server may be abroad, not directly providing Indian Standard Time.

For demanding applications, satellite links are used for highly precise time transfer. The CSIR-NPL has commissioned a White Rabbit Technology-based IST Dissemination Demonstration Network in Bengaluru, which uses an open-source networking technology to synchronise computer clocks over fibre-optic networks. This ensures that clocks in different locations stay synchronised with IST.