[nickjj]

What if you switched to a part time job that let you take care of the bills without dipping into any retirement funds?

That would give you the option to work 20-25 hours a week for your main part time job and then another 20 hours a week for your start up idea while still working ~40 hours a week.

Personally I would say it's well worth spending a couple of years trying that out instead of going down the path of 12+ hour work days with a family.