My guess would be Firefly’s browncoats. Their canon is fifteen television episodes and one movie. By my calculation, you could watch the entire canon in 749 minutes - just under thirteen hours.
Star Wars might be a close contender. But even if you count the canon as just the six movies, you’ve got 802 minutes. And realistically, you have to add the television series and at least some of the specials.
The Prisoner (another series I thought might be the winner) had seventeen 52 minute episodes and added up to 884 minutes of viewing.
Other cults like Star Trek, Dr Who, X-Files, Star Gate, Babylon 5, Battlestar Galactica, or Buffy don’t come close - they ran for years and the episodes and/or movies added up.