@otowa You can submit it in any state. However, while it doesn’t have to be finished, it would be better if there’s enough to give feedback on.
With that I mean, if you submit a half finished model (like a car with just half parts done) then the instructors can only give you a few small remarks. But if your modeling is finished, and even better you have your base materials/textures applied, they can advice you on how to take it to the next level. And if you’ve also got a basic composition and light setup going on, and maybe added some details like wear and tear, then they can really dig into it!
The more finished it is, the more valuable their notes will be. Hope this makes sense.