While a single use of the item will take a brand new level 1 follower to just over level 14, you won’t be able to level up all your followers this way without an obscene amount of anima, as they need a grand total of 395,250 to cap out at level 60. Because this means you’d need 790,000 Anima to buy enough Timebound Ruminations to level a single companion that way, the item is more intended as a supplement and extra anima sink than to replace the leveling grind entirely, as fully leveling all 20 non-shared followers after swapping to a completely new covenant would require an astounding 15.8 million anima. The Wisps of Memory is also another good way to jumpstart adventurer levels, awarding 75,000 experience to take a level 1 hero to level 38, but the item is limited and only available as a reward upon reaching Renown 52, 67 and 76.
Here’s some details on how much Anima you would need to power-level your followers:
- 1 Follower from 1 to 30: 80,000 Anima
- 1 Follower from 1 to 40: 180,000 Anima
- 1 Follower from 1 to 50: 400,000 Anima
- 1 Follower from 1 to 60: 790,000 Anima
- All 20 Followers from 1 to 60: 15,800,000 Anima
This chart made by redditor jmxd graphs the amount of experience needed for a single covenant companion to reach level 60.