The reason why this was announced at 3:30 am ET will not be discussed.
The third in Nintendo's series of Partner Showcase videos has been announced.
The seemingly monthly series of videos will air the latest entry tomorrow (September 17) at 10 a.m. ET, 7 a.m. PT, 1500 BST, and 1600 CET.
No indication of any announcing companies has been made, though the timing is consistent with announcements prior to the Tokyo Game Show whose online version runs next week.
Tune in 9/17 at 7 a.m. PT for a livestreamed #NintendoDirectMini: Partner Showcase, featuring information on upcoming #NintendoSwitch titles exclusively from our publishing partners. pic.twitter.com/nidlz0AnWV— Nintendo of America (@NintendoAmerica) September 16, 2020
UPDATE: The original announcement of the Showcase was made during Nintendo's corporate policy briefing.