There is none.
At least for me anyway.
I did a short presentation at the New Venture Design class that PeerFX originally came out of on Tuesday night. I have to admit it feels awesome to know that I'm sharing my little tidbit of lessons with an aspiring group of students in the audience.
One thing though. There were repeat questions related to this "work life balance" thing. The standard answer from a speaker would be it's important, we all take vacation here. What we don't tell you and what I did tell them was "It's tough as heck in the beginning of starting your business, so wave BYE to vacations and put in the required hours to get where you want to be."
In my opinion, you can take as much time off as you wish, it's just a matter of how long it will take for you to get where you want to be. You want to work the 9 to 5 instead of 9 to 9. Great. Go right on ahead. Just expect that it will take you 6 years instead of 3 (I may be exaggerating I may not).
If you want one thing, quite often you give up another because you only have so much time in one day. Do you want your business to grow or more time to veg in front of the tv?