It seems the Japan Professional Baseball Players Association (JPBPA) asked the NPB to re-consider scheduling outdoor day games in the middle of summer when temps are really high (particularly in July) to night games next season. The JPBPA apparently received some complaints / feedback from players about how difficult it was to play in the hot weather. There was also some concern about the comfort of the fans watching the game as well.
While the NPB understands the difficulty surrounding games played in extreme temps, they also feel day games are important and may try to work around the issue to scheduling outdoor games to a later time (like around 3pm).
The issue will be brought up again during the 12-team meetings on the 6th (teams ultimately decide game start times).