in case you didn't know, which I believe you do from this, the picture indicates it's supposed to accelerate building time. Weird, that's never happened to me haha
I haven't used it yet but plan on doing the quest that gives it as a reward. Maybe if I can prove that's what it said then the mods will have to give me exactly what the rewards says. 30% attack bonus would be nice.
Now if only the Grepolis gods would give me some huge reward for finding something amazing like this...