What does "he was likely to be in the sixth year before he finished it" in harry potter mean?

Question

Snape had given them so much homework, Harry thought he was likely to be in the sixth year before he finished it. Ron was just saying he wished he had asked Hermione how many rat tails you were supposed to be add to a Hair raising potion when an angry outburst from the floor above reached their ears.

Harry potter and the chamber of secrets

I don't understand the bold part, "he was likely to be in the sixth year before he finished it." 

Does it mean "the homework was too difficult for Harry that he thought he'll be able to finish it by his 6th year in hogwarts"....?

Answer 1

Actually, No.

It's not the complexity that he's thinking about, but the sheer quantity of homework.

Snape had given them so much homework, Harry thought he was likely to be in the sixth year before he finished it.

This simply means that Professor Snape had given him ginormous amount of homework, which would take Harry 4-5 years to finish. I'm assuming it would take him that many years because Harry was already in his 2nd year at Hogwarts in Chamber of Secrets (if I'm not wrong).

Answer 2

Varun Nair's answer is mostly correct, but he misses the part where the expression is just an exaggeration for effect. Snape didn't really give them so much homework that it would take four years to finish; Harry just felt like it was a huge amount.

Similar examples of exaggeration for effect:

The cafeteria prices have gone up so much, I might have to sell a kidney just to be able to eat there.

Next semester I'm going to have to rob a bank to buy my textbooks. How else do they expect a poor student to pay for them?

She ate so much at the buffet she felt like she couldn't move. "They're just going to have to turn me on my side and roll me out of here," she thought.