I'm sorry I didn't see this egg in the massive Egg Guide [removed url] maybe I'm half asleep. Honestly I'm a little embarrassed because I don't know how it ended up in my nest. (Sometimes I'm half asleep when I play, and maybe I accidentally "activated" one of my 84 dragons in storage!) Anyways, it is 24 hour egg, but there's a small small chance it may be more; the green timer bar was barely started at 23:35.
