Studies show that chronic overwork leads to stress, which causes a number of health problems. Working all the time diminishes your ability to engage in interpersonal communication, which is essential in many roles. You're more likely to make mistakes and poor decisions when you're tired, which is often what happens when you consistently work long hours.
Give yourself working restrictions. Set a standard number of hours to work each week. Research shows there is no benefit to consistently working more than 50 hours a week, so make it 50 or less. Then, work backwards.
What are the most important things you have to get done to advance your business? Once you've got your list, write down how much time you need to do those things and block off the time to get them done.