Fortnite servers downtime usually lasts around 2 to 3 hours on average during scheduled maintenance or updates. For recent updates such as the v37.40 patch, the downtime started around 1 am PDT / 4 am EDT and lasted approximately 2 hours before the servers came back online. Downtime times are scheduled to minimize disruption and matchmaking typically ends about 30 minutes before actual downtime begins. Thus, when Fortnite servers go down for scheduled maintenance, players can expect the game to be unavailable for roughly 2 to 3 hours, sometimes a little less or more depending on the update's complexity. This aligns with usual practice to quickly roll out patches and fixes so players can get back to the game as soon as possible.
