I have learned a lot about this from Benedictine nuns and monks. According to Rule of Saint Benedict time should be equally divided to work, prayer and relaxation. A bell is rang to remind everyone when its time to begin the next segment of the day. Benedictine monastic "enterprise" managed to thrive this way 1500 years with happy nuns and monks.

There is always room for flexibility, particularly when we get inspired to perform a certain task and do not wish to get interrupted. In our own business, especially if this is the right business for us, we tend to go into flow during our work. In this state we lose track of time and we do not get tired. We can allow ourselves to go into flow from time to time in some of our projects.
We may also wish to increase our working hours, for example when our business has just entered the stage of rapid growth.
However we can be much more efficient and provide better quality service if we limit our work to a reasonable number of hours.

In an average day the best option is to plan not only work but also leisure activities, keep photos of your loved ones on your desk and set up reminders in your watch or phone. This will be like imitating life regulated by a Benedictine bell, which can be helpful in fully enjoying all the aspects of your life.

Feel free to contact me if you have more questions. 
I'm an Industrial Psychologist specialized in personal happiness and life satisfaction.
I can also can help you find the right business idea which will bring you the flow experience and make it easier for you to become successful.