That's still plenty respectable. Woz designed most of the Apple II in his apartment while working at Hewlett Packard. However, (if my memory serves me correctly) he left HP to put the finishing touches on the design before it launched.

So perhaps it might be best to leave when your product is about 80% to the point of launching, because then you can focus full time on actually getting it out the door, and on the aftermath. If you have a day job, it might never seem like it's ready to launch.

But that's just my hypothesis; I don't have any actual experience with that. :)