The reason why this was announced at 3:30 am ET will not be discussed.
http://www.nintendoworldreport.com/news/54937/next-partner-showcase-direct-airing-thursday
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.
UPDATE: The original announcement of the Showcase was made during Nintendo's corporate policy briefing.