I do not hate my job, I just feel that I'm not using my full potential there. So, 'slogging away' is an strategy that I abide rigorously so far, but when should I stop? =)
Yep, I am using equivalents of Vanguard, but I do not really look for FIRE as a solution. There are also risk even in 'risk-free' investments.
Since you mentioned wanting to work on a product though, I suspect one more year runway will decrease your chance of failure significantly (like maybe in half). But I'm so risk averse you probably should never listen to my risk assessments...
I do like a lot of the comments suggesting working on the next thing for a while before quiting your high paying job (maybe even try to take a month off after your next project). I know your free time is at a premium, but there are a lot of things that just take calendar time when starting a business. Things like waiting for government papers, or responses from prospective customers. It's nice to be earning money while some of that is happening.