Question... what kind of shithole did you work at before where a judgmental boss who demands OT every day, arbitrarily fires people, is unwilling to listen to ideas for improvement, and demands you make up extra OT for leaving on time all while running an unstable business is "much better".
My god that must have been a horrible place to work.
As to the question, I have left a job after 5 months because it was about as bas as the job you describe. It looks bad on a resume, but if you otherwise have a stellar work history(long list of references, no other jobs < 2 years), no one will care.
Also, we are pretty much at full employment in the US. Good bet that you will never have a better opportunity to find a company that is a good fit, especially in a niche position.