My advice is: try doing something on the side first, something that people can actually use, share it with friend and see how you feel about feedbacks. I found for myself that the greatest motivator is your will to build something useful; your major test will be how you bounce back from negatives.
How many hours you put in, when do you work even whether you should leave your job or not will depend of your level of motivation, it’s hard to build a startup without sacrifices.