There have been many leaks suggesting there will be a live New Years Event in-game and it seems that it has already gone live.

Epic Games have been very successful in the past for pulling off in-game live events in Fortnite. Players worldwide are able to witness a one-time only event live at the same time, which was unheard of in other games.
Data-miners have leaked sound files for an event that is supposed to be taking place on New Years, however, it seems players have already witnessed the New Years Event in-game.
There will be a disco ball in the sky and a count down from 10 for the New Year, along with fireworks to bring us into 2019.
I just wanted to get the S, then this happened
byu/ibrahim210105 inFortNiteBR
It also seems like players will not be able to kill each other when the countdown is over, as all players will be forced to dance.
Mark Rein, Vice President and Co-Founder of Epic Games, has tweeted the following:
It’s already New Years Eve in the Christmas Island, in the country of Kiribati and it will soon be New Years Eve in Fiji. https://t.co/pJKMaPIatB
— Mark Rein (@MarkRein) December 31, 2018
It seems like the event will be showing when it’s the new year for each country and it was not a mistake as some thought.
The official Fortnite Twitter account had tweeted the New Years Event with Ninja and had stated that the live stream would be taking place at 4pm EST, so it is possible there could be more added at this time.
https://twitter.com/FortniteGame/status/1079482286809198594
It was known previously how Epic would pull this off, due to the different time zones, however the event is taking place for every time zone. Happy New Year!