That may depend on the instructor. Some instructors use the first day of class just to go over the course and expectations, and they do not start teaching until the second day of class. Others jump right in on the first day, and if you have not already started reading, you may already be a day behind. There are others who assign homework on the first day of class. I suggest examining the course syllabus before the start of the term (if it is available), and deciding then if you need the book(s) right away. If you order the books, you also need to account for delivery time, which could put you further behind.