In my opinion, the more important events (and this is definitely the ritual) should in no way be limited in time. The ritual has consequences. It is the same with the potential loss of a companion.
You already have some time-related events, but they are not very important, and some completely irrelevant npc will die here. In my opinion, it should be like that.
Why SHOULDN'T the ritual be limited by SOME sort of time? Is it REALLY important to you getting rid of the tadpole? Seems more like a side quest you don't have to do anything about - not really. In fact, MOST of EA is side quests. So why not have a few "timed" events?
Now, again, by this I mean after X number of days, SOMEthing happens. Using the ritual as an example, let's just say it takes 3 days to complete. You Long rest 3 times after going to the grove. Someone tells you, "The ritual was almost complete, but Rath interrupted it. Now he is locked up and it's starting all over. You have 3 more days."
Something LIKE this would allow plenty of time to complete the quest and yet would make players go, "Oh dang! Best not spam long rest."
