A word of warning here. When I grew up my parents weren't around much because of their business. They did allright businesswise, but my brother and I grew up very independent. Not neccessarily a bad thing, but we don't have a strong bond. This is something I didn't realize until I met my wife, and her amazing family.

What I'm trying to say is: if you don't make sure your work/life balance is balanced right now, it probably won't be balanced in the future. And it probably will leave a mark on the bond between you, your spouse and your children. Realize that you can never get back the time watching your children grow up.

We're in the same situation. I'm also in my mid-30's, two kids, a job and a mortgage. I spend my commuting time on my startup, and all the time I can get when everyone's asleep. It was hard at first, but now I have developed a routine that works for me. I may not be able to work as many hours on my startup as someone with less obligations, but the hours I do have I spend incredibly productive and efficient. I love working on my startup, but until it makes enough money for me to quit my job, it's family first, startup second.