The two countries on the divided peninsula have had different time zones since 2015 when the North suddenly changed its standard time to 30 minutes behind the South.
Pyongyang cited a nationalistic rationale, saying it would return the North to the time zone used before Japan's 1910-45 colonial rule of the peninsula to mark the 70th anniversary of its liberation from Tokyo.
But Kim promised to change the time zone back during the historic summit with South Korean President Moon Jae-in, Moon's spokesman said.
The pair held the summit -- the third such meeting between the two Koreas -- at the border truce village of Panmunjom, during which Kim set the foot on the south side of the border for the first time and the two leaders pledged to pursue denuclearisation and a permanent peace.
Kim said he found it "heartbreaking" to see the two wall clocks hanging at the summit room showing different times for the two neighbours, the spokesman Yoon Young-chan said.
Yoon hailed the move as a "symbolic move" for better ties between Seoul and Pyongyang.
The creation of "Pyongyang time" drew criticism from Moon's conservative predecessor, Park Geun-hye, for further deepening the disparity between the two Koreas whose division was sealed by the 1950-53 Korean War.
The two countries have remained at war technically after the war ended with an armistice instead of a peace treaty, and Moon and Kim on Friday vowed to seek the formal end of the war.
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