The start time of the marathon, the event with the longest duration outside, was likely to be brought forward by one hour to 0600 local time (2100GMT) to avoid the highest temperatures, Japanese broadcaster NHK reported on Wednesday.
The original start time was 0700 for both the women's marathon on Aug. 2, and the men's event scheduled for the final day of competition, as per tradition, on Aug. 9.
Tokyo 2020 President Yoshiro Mori had previously requested Japan's Prime Minister Shinzo Abe to adopt daylight saving time in order to host events in cooler hours.
However, NHK said that a panel of the governing Liberal Democratic Party have abandoned these plans.
"We understand the ruling party of the national government held a study group meeting today where it was decided that it is difficult to submit a bill at the ongoing extraordinary session in the Diet (Japanese Parliament)," a Tokyo 2020 spokesman said in an email to Reuters.
"We understand this means it is challenging schedule-wise to introduce daylight saving time in 2020.
"Based on the judgement of the ruling party, we would like to continue discussing the measures, including competition schedule change with the IOC, International Federations, National Federations, Tokyo Metropolitan Government and other related parties."
Tokyo 2020 vice-president Toshiaki Endo, Japan's former Olympics minister, was quoted by Kyodo news agency as saying the organising committee would formally propose the marathon time changes to the IOC.
Temperatures in Tokyo reached a record 41.1 degrees Celsius (106 Fahrenheit) this year, with the July average reaching more than 30 degrees since 1998, according to the Japanese Meteorological Agency.
(Reporting by Jack Tarrant; Editing by Chrsitian Radnedge)
