The goal is to get something that's going to extend that six months, whether it is convincing investors to contribute to your venture or convincing customers to give you a dollar. Ideally you can do both, but if you can't do either with the full force of your time then something is off and you should shift your efforts.

I think six months is good because it is enough time to figure out if something isn't going to work while being short enough to not be an insurmountable challenge to save up for. I don't have a family yet so there is bias in that number, I would probably say 12 months if I was helping to support one.