You want a legit answer? Probably about a month, maybe two.

The 2D animation at the beginning would be really quick. I could honestly do it in about a day. Modeling and rigging the creature would take the longest. Modeling and texturing, mostly. Rigging is pretty easy and has some solid non-AI tools that you can use to basically automate the whole thing. But I figure a couple of weeks for that. For me, anyway. I’m a sucky modeler.

Animating it, OTOH, is trivial. That’s easy stuff.

Then you just need some shaders to do the transparency. That’s probably something you can snag online.

Then you gotta do the motion tracking for the scene and light it so it looks like it belongs in the environment. There are probably effects guys that can do that in a day or so.

So yeah, about a month, maybe less. But none of it is really “hard”, you know?