Stick with the company for at least a year. You'll learn a lot of valuable skills. Staying with any one employer for at least a year makes it more likely you'll get hired somewhere else. Also everyone wants to know how many years, not months of experience you have with each skill you claim to have.
Be advised that it is quite uncommon for startups to actually succeed. The chances are quite good that your stock options - if any - will not be worth anything at all.
Do the very best you can to stay connected - or GET connected - with a professional network.
Take a long, hard look at whether your startup really will succeed. If you don't think it will, start sending out resumes towards the end of your first year on the job.
If you really do believe it will succeed, then decide for yourself whether it is worth all the effort and sacrifice.
Find some older, more experienced industry people who can give you some insight as to whether your startup will succeed.
Leave the office at least once per day, preferably twice, to go get a coffee or a smoothie. Do this on your own sometimes, so you can think, or invite a colleague. If you never leave the office during such a hard workday, you will burn out for sure.
Say you're having trouble on some code. Ask your boss out for coffee then discuss your problem with him. At Working Software, my boss and I did that every single day for three years.