https://www.gamespot.com/articles/fortnite-servers-down-for-maintenance-update-compl/1100-6460503/

Fortnite servers have been taken offline for another round of maintenance, Epic Games has confirmed. The developer hasn't revealed how long the maintenance will last, but it's began at 1 AM PT / 4 AM ET / 9 AM BST and affects players on all platforms--PS4, Xbox One, PC, Nintendo Switch, and iOS. [Update] Maintenance has been completed and servers are live again; original story follows.

Beyond the start time, Epic hasn't shared any further details on tomorrow's maintenance, but these periods are typically followed by a new batch of content for Battle Royale mode. That will likewise be the case, as the second set of weekly challenges for Season 5 are slated to roll out on July 19.