Apparatus of Kwalish- Help needed!

I'm running the Lost Laboratory of Kwalish for my friends as part of my campaign. In the treasure that they find, there's blueprints and materials to build this thing called the Apparatus of Kwalish, which is basically a tank with claws.

I'm basically needing help with how much time they would need to craft it, since it doesn't exactly make sense to me to have it already built in the treasure hoard.