Success! All players can now join in on the fun in the Playground LTM. Drop in and let your imagination run wild.— Fortnite (@FortniteGame) July 3, 2018
More details: https://t.co/nSpL6uQDwl
Epic Games also took to Reddit to explain a little more, promising to release an in-depth, detailed postmortem to let its players know about the obstacles it encountered when it initially enabled the limited time mode. The post reminds players to change their region back to "auto select" and to keep trying to join the queue if at first they don't succeed. There are likely lots of people trying to get in at the same time.
Playground is basically an instance of the Fortnite map that will host up to four players at a time. You'll get an hour to practice all your building and tactics before the deadly storm starts shrinking during the final five minutes of the match. You'll be able to shoot your teammates in this mode, too, for a little friendly competition, and you'll get unlimited respawns when you're shot. Resources are also more plentiful, and you'll be able to gather them at 10 times the normal rate. There are a ton of llamas, chests and ammo boxes scattered about, as well, to keep you well-stocked as you play.