They shouldn't tie anything to fates.

Having the books tied to fates does nothing. He'll it doesn't even have a lore behind it.

Instead being tied to specific fates make the players clear 5 fates in each area of the book (set 3 areas to do one book in) this way we have no reliance on timed spawns and yet another reason for high level players to be assisting with low lvl fates.