You need to set regular work hours, and stick to them. The reasons for this are twofold:
1. Your customers / co-workers need to know when they can reasonably expect to contact you. Providing them with a schedule of your work hours gives them this. This doesn't mean that you should never work outside of these hours -but those times should be the exception, not the rule. This echoes the need for communication and professionalism.
2. Your family / friends need to know when you will be "at work", and when you will be "at home". This not only helps them and you emotionally -but it also lets them know that when you are "at work" you should not be interrupted (within reason). Your friends and family may not understand the demands working from home places on you. You must be clear and firm about this, or it will emotionally overwhelm and physically exhaust you. Setting specialized hours is NOT unreasonable (such as having a daily extended time to pick up the kids from school, run to the bank, do a load of laundry etc) -provided that all concerned are aware of these specialized hours. Again, this falls back on communication and professionalism.

Are you beginning to sense a pattern here?