Ten minutes used to be the cutoff where you could provide an interstitial advertisement. This sort of turned into a sort of wive's tale, where people thought th

Ten minutes used to be the cutoff where you could provide an interstitial advertisement. This sort of turned into a sort of wive's tale, where people thought the algorithm would push such videos. It's not the case today. The reason that 20 minute videos are more popular these days is that more people are watching youtube on larger screens, like on their TV on the couch, and so more reliably watch longer videos than in the past.