How long is the Diablo Immortal story campaign?
Diablo Immortal has provided more information on the length of the story campaign and how to structure it, among other things.

In an exclusive worldwide interview, he talked to two leading developers about Diablo Immortal. Wyatt Cheng (Game Director) and Joe Grubb (Chief Game Designer) provided more details on the length of the story campaign and how to structure it, among other things.
Diablo Immortal will likely be out in the first half of 2022. During the last beta testing phase where MeinMMO took part, the MMORPG was already very fluid. Our impression after testing was that the only thing missing was fine tuning. So the release shouldn’t really take much longer.
The main story can be completed in under 10 hours if played linearly.
Wyatt Cheng and Joe Grubb made the following statement about Diablo Immortal’s campaign duration;
You could see that he didn’t mean to say anything wrong here and it wasn’t easy to guess the exact length. Because MMORPG does not offer a linear experience in this sense.
Wyatt Cheng explained how the story campaign was created: “Different people need different durations. I hesitate to answer because our story is structured with 8 regions. But you can’t teleport to the area and play the story and then finish it.
The story in each area takes about 15 to 45 minutes. Or let’s say about half an hour. But each has a level cap. Gut Swamp, for example, is for level 40-45. So when you reach level 40, you can experience the story that continues the story of the previous region and then continues there.
When you complete the main story quest in this area, you will find other activities such as Elder Rifts, Bounties or Dungeons to gain enough EXP to reach the required level for the next area.
If it was just the story without any level, you’d probably finish it in under 10 hours. But there is all the other content you can do.”
“Immortal, the biggest and most ambitious Diablo ever”
Chief Game Designer Joe Grubb added that there will be more story content than just the campaign:
“Immortal is the biggest and most ambitious Diablo ever. So it’s not just a questline, there’s a lot of content around it. Plus, story-driven content like side quests with the characters you help. It really depends on how much you want to get into. If you ignore all that content, it goes pretty fast. But if you want to experience the Immortal fully, it’s a much bigger experience.”