The events had been scheduled to begin at 7 a.m. but with temperatures reaching over 40 degrees Celsius (104 Fahrenheit) last year, organisers were under pressure to make changes.
This was to ensure the safety of athletes and supporters.
The 50-kilometre race walk final has also been moved to 5.30 a.m. local time to avoid the midday sun.
A record heatwave last year killed over a dozen people in Tokyo with July average temperatures reaching more than 30 degrees for the first time since 1998.
This was according to the Japanese Meteorological Agency.
Athletes focus on developing a strong circadian rhythm to perform at their best during competition and will have to amend their schedules for this ultra-early start time.
Tokyo 2020 organisers said the changes had been ratified by the International Association of Athletics Federations (IAAF).
‘’We have an approval from the IAAF athletes commission. So, it is understood we have approval from athletes,” said Olympic gold medalist Koji Murofushi, who is Sports Director at Tokyo 2020.
The schedule was also noticeable for the number of finals taking place in the morning.
This was partly due to the heat as well as considerations for U.S. broadcasters wanting showpiece events in prime time.
Nine athletics finals will be held in the morning while basketball and swimming will also feature medal events in the morning.
“Also, I hear that athletes are saying it is possible to condition if they know the schedule in advance. So, I think that they should condition themselves to do their best at Games time.”
Women’s softball will be the first event of the Olympics, in Fukushima on July 22, two days before the Opening Ceremony.
The women’s 10-meter air rifle is the first medal event of the Games, starting at 8.30 a.m. on July 25.