https://www.cnet.com/news/fortnite-fortnitemares-event-is-coming-to-an-end-sunday/

It's scheduled to occur just after Fortnitemares ends, and nobody (except Epic) knows what's in store for the game afterward. The only thing we know for sure is that if you're a diehard Fortnite fan, you'll want to be in a match during that time Sunday.

Obviously you're going to want to be in the game, but it's also wise to be prepared so you have the best chance to see everything that goes down. Make sure to power up your device well beforehand and install whatever updates the games needs (especially true for mobile devices) so you're ready to go. To be safe, you might want to start matchmaking about 5-10 minutes before to make sure you're in the game on time.