Often there is a bell shaped curve where productivity peeks at a point and bigger efforts after that make you actually less productive overall. In my personal experience most projects are a marathon not a sprint. Always sleep the 8-9 hours necessary to feel full-rested. I'm most productive in the morning so I try to work every day during mornings but since in the afternoon I'm a lot less productive I've decided I can allocate that time to entertainment and social activities. My entertainment and social activity tend also to be along learning new things.