The average speed for copyediting is around 1,000 to 2,500 words per hour, so for an 80,000-word book, you're looking at between 32 and 80 hours of work. Proofreading is usually faster, around 2,000 to 4,000 words per hour, which works out at 20 to 40 hours of work for that 80,000-word book.