Epic has announced tweaks in the way engagement payouts for developers publishing as part of Fortnite’s creator ecosystem are calculated.
In a blog post, the company announced that it's added a 'time played' metric, which "reward creators for the time players spend in their islands."
Popularity and retention remain part of the equation as well but Epic announced that it's "decided to lower the weighting of these metrics in engagement payouts for now" and instead to boost the new 'time played' aspect.
source https://www.gamesindustry.biz/epic-tweaks-engagement-payout-metrics-in-fortnite