https://www.gamespot.com/articles/new-fortnite-update-coming-tomorrow/1100-6458346/

Fortnite's next update is coming soon. Developer Epic Games has announced that the v3.5 update will go live tomorrow, April 19, starting at 4 AM ET / 7 AM PT.

Epic no longer shares patch notes ahead of launch, but these will be available once the update goes out tomorrow. Epic said the patch notes will be published "once downtime begins," so we also know there will be a period of downtime as well. However, it's unclear right now how long the servers may be offline for.