Nintendo performed maintenance on its network servers for Switch and 3DS on November 21st, but it looks like there’s more work to be done. Another round of maintenance (exclusively for the Switch this time) has been scheduled for the wee hours of November 23rd/24th. This maintenance will render the online multiplayer of “some software” unavailable.
Here’s the schedule:
NOVEMBER 23rd, 2017: 11:50 PM to 2:30 AM (Pacific)
NOVEMBER 24th, 2017: 2:50 AM to 5:30 AM (Eastern)
Unless you’re the type that likes to game in the middle of the night (or you live in an extremely different timezone), these maintenance times shouldn’t affect you too much. But, if you do happen to have a lot of late-night gaming sessions, just be sure to keep these times in mind.