What your doing is actually recommended. Studying for short periods of time and digesting smaller amounts at a time. This works well especially for people with Adhd etc.
This book is a great read and has a great chapter on procrastination.
https://books.google.com/books/about/How_to_Become_a_Straight_A_Student.html?id=Ecl4xUM5SwMC&printsec=frontcover&source=kp_read_button