No, You dont have to quit your present job for bitcoin. You can do it both, your present job at day time and bitcoin after your work. Because you will never know if until when the bitcoin is but your present job and if you are regular then you can be sure to have it until your retirement. So i suggest to choose both.
Yes, I agree with that. Bitcoin is all about business and we are not sure if it is long term or not. So, I recommend not quitting of job, but rather doing both. It's just a matter of time management. We can do or explore more about bitcoin after rendering duty.