North Korea went forward in time by 30 minutes on Saturday, state media said, to match its clocks with those of the South following last week's inter-Korean summit.
Leader Kim Jong Un promised the move during the meeting at Panmunjom in the Demilitarized Zone that divides the peninsula, when he and the South's President Moon Jae-in pledged to pursue denuclearisation and a peace treaty.
"The time-resetting is the first practical step taken after the historic third north-south summit meeting to speed up the process for the North and the South to become one," said the official KCNA news agency.
In Panmunjom, Kim had said he found it a "painful wrench" to see clocks at the summit venue showing different times for the two neighbours, KCNA reported earlier.
Kim expressed "his resolution to unify the two times... as the first practical step for national reconciliation and unity", it said, and the North's parliament on Monday adopted a decree to put the move into effect from Saturday.
Seoul welcomed the decision as a "symbolic move" towards better inter-Korean ties.
North and South are now vastly different societies, one a democratic member of the OECD club of developed countries, and the other an impoverished, hereditary one-party state left isolated by its pursuit of nuclear weapons.
But it was only in 2015 that the Koreas' clocks diverged, when Pyongyang put itself back 30 minutes to return to the time zone used in the peninsula before Japan colonised it in 1910.
As of Saturday, Seoul, Pyongyang and Tokyo are all in the same time zone.
North Korea is not the only country to have used time to assert its national identity.
China and India have both imposed single time zones to promote unity across their vast territories, with people in China's westernmost provinces officially keeping to Beijing time despite the sun rising and setting two hours later than in the capital.
Most time zones around the world are an hour apart, but some have smaller differences - Myanmar is half an hour behind next-door Thailand, while Nepal sets itself 15 minutes ahead of India to assert a difference from its giant neighbour.
And despite lying on Europe's western edge, mainland Spain has been in the same time zone as central Europe since 1942, when Francisco Franco's fascist government adopted it to line itself up with Nazi Germany.