That's entirely up to you. It's your company. Startup life in general is probably going to be busier than working a corporate job, but the answer is: whatever the company needs. Sometimes that will be 80 hour weeks, and sometimes you can do 40 or take a vacation (which you should do from time-to-time anyways).

In my opinion, you should do everything you can to maximize your valuable time during the YC batch, so it'd make sense to work harder then. But even a startup is not everything in your life. If you have a family and kids, those need time also.