https://www.pcgamer.com/fortnites-time-limited-blitz-mode-is-now-live/

"Blitz," a limited-time game mode for Fortnite that promises "faster and more intense matches," is now live. Blitz mode matches feature boosted treasure and ammo spawns, increased resources and health, begin with the storm circle already closing in, and are capped at a maximum of 15 minutes in length. 

As detailed in the 3.3 patch notes, here's a more precise measure of what you can expect: