Fortnite is gearing up for a big season event this weekend, and the word is that it will be something you can actually miss if you’re not careful.

If you’ve played recently, then you know that Fortnite is hinting that something is happening soon. For one, there’s a timer that is displaying on certain in-game TVs — and it’ll reach zero at 1:30PM EST, this Saturday.

You may have also heard that the game is blasting a siren near its evil super villain lair. This location was introduced in season four, but as of yet, Epic has yet to do anything with it.

We do know, however, that the area holds a giant rocket, so the leading theory is that Epic will launch it into the sky. While this seems likely to happen on Saturday, we don’t have a sense of how this will change the game, if at all.

Big in-game events are nothing new for Fortnite — last season ended with a comet impact that changed the map — but this one is going to be very different. According to major Fortnite YouTuber Muselk, whatever event Fortnite is planning this time around will only happen once, in real time. The Verge has also heard similar rumors.

Meaning: if you’re a Fortnite player, you’ll have to be logged in and in the game at a specific time and location to see the event unfold. If you’re not participating when it happens, you won’t get to see it in-game: you’ll only see the result. This is a major departure from the comet event, which was visible for weeks and had its climax whenever you logged into the game. This is, however, yet another example of Epic Games innovating this space with Fortnite existing as a living, breathing live game. It will literally be a “you had to be there” festivity, though of course, people will likely record it for posterity.

Hopefully the servers can take everyone logging in at the same time. And for those of you who haven’t visited the rocket yet: it’s by a mountain near Snobby Shores.