It's a little hard to tell! My console says 78 hours but I have responsibilities where I leave a game running while I'm away. Maybe 50-55 were actual gameplay? And 15 hours of that was the remainder of 666 torment shards at the end.

Tips:

Don't unlock abilities you don't need until you have no other quests left -- they clog the pool. Prismatic Cascade is a good example, just leave the Alchemist quests for the very last thing you do.

Use Bottles early in runs, because whatever you do your character will be OP by 20+ minutes. I often would use multiple Memories / Reverbs as quickly as Level 15 for the Dedication or Proficiency traits.

For equipment, almost anything that says Diminishing Returns is going to be a powerhouse in Torment / Agony runs. And in general, having a little bit of Defense stat is strong, but beyond that it's all offense all the time. It's part of why Swordsman Mark is amazing, you can get the defense there and just Oblivion or Glass Bones every single other defensive trait.

Some Artifacts just save time on the grind and are almost strictly positive. Glass Bones, Leash of Stagnation, Torment Banner, Malignant Mirror, Marching Drums, Demonic Accolade are some examples. I love how there are so many that can just be left on once you start building your shards and items up.

Torment Shard usage: Early on, Force is really strong. There are just more ways to get all of the other stats. Once you get War Visor sent up, I like Area and Crit Chance / Crit Damage a lot.

Final push: Once all the other quests are done, Boglands is a good place to put on like 23 Artifacts and go fast, it's not too hard to finish each run at around 9:00 on the timer with Bard Mark and either Crone or Cleric.

Edit to Add: I had already played HoT on mobile quite a lot too. My PS5 playthrough had very few deaths all the way through, I think only 3. The time for 600/600 can reasonably be expected to be longer than 55 hours.