If you want to complete your daily NeoPass Quest Log tasks, make sure you do it before 6pm tonight!
TNT did not state what the maintenance was for, but in the past it has signified the start of a new in-app event.
In unrelated news: a Valentine's Day gift is available through the app! This was originally promised for logging in on February 14, but didn't work for most players, so the award period has been extended. Check your notifications for a letter! You will receive an in-app profile frame and (eventually, it seems to take a while) a pair of items on Neopets.com:
