There is no official uptime from xingwang's blog

There's more content coming to Fortnite: Battle Royale, and the game will be going down for a little while to Cheap Fortnite Items accommodate it. Fortnite servers are currently scheduled to go down for maintenance at their usual time of 4:00 AM EST for the v3.5 content update, with patch notes being made available as soon as downtime starts. There's no official uptime, but it usually lasts for an hour or two even if last week saw an impressive outage that stretched for nearly 24 hours. We'll have more when the patch goes live, but we're hoping it goes a bit smoother than last week.

The only thing that we know for certain we'll be getting with v3.5 is the Light Machine Gun, which showed up in the news feed yesterday. The Light Machine Gun is available as a green, or uncommon, item, meaning that we'll see a lot more of it than recent Legendary and Epic items like the Port-a-Fort or Heavy Shotgun.