Update:Epic Games have tweeted about the "Unlocks in 0 Seconds" message, describing the problem as a known issue that was intentional so that they could push the weekly drop until Thursdays.
Here's what they said:
KNOWN ISSUE: Week 5 challenges available in 0 seconds.— Fortnite (@FortniteGame) May 29, 2018
Week 5 challenges will be available on 05/31 at 4am ET/8am GMT.
This was an intended change to push back Weekly Challenges to Thursdays.
In Fortnite season 4, every Tuesday hundreds of thousands of players parachute out of the Battle Bus to voraciously devour the week’s Challenges. However this week there seems to be a bit of a delay, with the Week 5 Challenges sat at “Unlocks in 0 seconds” for everyone.
Right now, there’s not much information to share. But take solace in the fact that yes, we’re all getting the same thing as you.
On twitter, the official Fortnite account hasn’t posted for the last nine hours at time of writing and the Fortnite status page - which reports any technical issues that the game is experiencing - says that there haven’t been any problems today:
Restarting the game application multiple times doesn’t seem to help, either.
We’ll update this page as the situation develops.
In the meantime, get a heads-up on what the Challenges will probably be with our page on the leaked Season 4, Week 5 Challenges.