Both Akili and Book Raid can affect each other's spawn time.
If Book Raid is ongoing, then Akili won't spawn. Akili will always spawn around 6:30 minutes after a successful Book Raid.
If Akili is ongoing, then Book Raid won't spawn. Book Raid will spawn around 2:30 minutes after a successful Akili, BUT if Akili finished after 15 minutes of the previous Book Raid, then the timer is unknown.
Graveyard is an event that happens when a previous event, "Defeat the Mordant Crescent before they Awakened buried Villagers", fails. That event fails quickly if nobody is present for a minute, so Graveyard is generally up