13/04
I did A small test yesterday, 22:11
and today 11:25 AM (even after server save) I still can't take a new one..
so its not based on cycle days.. this information of once per cycle looks wrong.
probably you can use it
I ll update here when I finally get my second one!
Edit
20 hours later (a little bit more)
19:08 You pluck a tuft of raven herb.
an instant later
19:08 At the moment you can't pluck raven herb here.
Edit 2 --------------------------
14/04
21:50 At the moment you can't pluck raven herb here.
So I don't think there is this break thing, whenever you use it you take the herb and enters the 20 hours cooldown