You buy books from term 1 first, then you buy term 2 later. Makes more sense to wait. Of course, you could
buy term 2 when you buy term 1 if you are 100% sure you know what you're taking next semester and you see a real good deal or a used book.
I know most people are advising to buy your books after you go to your first class, but I'm going to be crazzzzyyy
and suggest the opposite. I prefer buying my books early because then I get to buy them used
and save myself 30-40% on textbook costs. If on first day of class the prof tells me that I don't need a certain book anymore, no biggie... I can refund textbooks and get my money back. The only thing you can't refund is custom courseware. If you wait till your first lecture to buy your books, all the used cheaper books might be gone.
Just a tip