I find that it’s unrealistic to think that we can just work endless hours. I’ve heard it said that we have a day phase and a night phase. Our brain can probably really only do about three to five hours of really difficult cognitive extraneous work. Real problem solving is just difficult once you get tired later on in the day. Knowing this we should plan for it and make sure to arrange to schedule the most difficult work in the beginning of the day, and do more casual passive research later in the day. Once you get too tired to work, read or watch movies. Spend time with others and socialize. Share ideas. Look to see what others are up to.
I also suggest keeping a list of books and movies that will help you to come up with ideas that pertain to your projects. This way you aren’t just reaching for whatever an algorithm suggests.