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"....?