On Friday, South Korean authorities called on the activists to immediately stop sending anti-Pyongyang leaflets to North Korea.
North Korea pushed back its standard time by 30 minutes in August 2015, claiming the move was aimed at removing the vestige of Japan's 1910-45 colonial rule of the Korean Peninsula.
Trump, speaking at the annual National Rifle Association in Dallas on Friday, says it was his "position of strength" that is bringing Pyongyang to the negotiating table.
Next week, an ICAO delegation led by Pacific Regional Director Arun Mishra and Director of Air Navigation Bureau Stephen Creamer will travel to North Korea to further discuss the proposal, along with "other air navigation and safety matters".
According to the Yonhap news agency, the incident occurred in the town of Paju near the border with North Korea.
Pyongyang has long wanted to see an end to the United States military presence and nuclear umbrella over the South, but it invaded its neighbour in 1950 and is the only one of the two Koreas to possess nuclear weapons.
Invited to the royal wedding? Pack your picnic
It's set to be the wedding of the year, packed full of Hollywood's elite and the who's who of the royal family . He even told the Daily Mirror: "She is giving the greatest performance of her life".
He tweeted on Wednesday: "As everybody is aware, the past Administration has always been asking for three hostages to be released from a North Korean Labor camp, but to no avail". The leaflets also denounce the North Korean government for their human rights abuses and defectors have vowed to challenge a ban on sending propaganda across the border.
ReutersDonald Trump has previously threatened to "destroy" North Korea.
"Chairman Kim... said two clocks were hanging on the wall in the waiting room of the Peace House", Senior Secretary to the President for Public Communication Yoon Young-chan said at a special news conference.
That event did not slow the North's nuclear drive, but the situation looks more upbeat this time, Hong Min, analyst at the Korea Institute for National Unification, told AFP.
"... Pyongyang time shall be reset into GMT+09:00 (30 minutes earlier than the present time) with the 135th degree of east longitude as prime meridian", the decree read.
"If they shake the alliance for the sake of denuclearizing North Korea", he added, "we will have an economic crisis before a security crisis".