Inspired by this comic? http://dilbert.com/strip/2015-08-03 Print that out and hang it by your office door! :-)
Read "Peopleware" to understand the problem and then decide if it is worth convincing your president to do something about the long hours or if you better look for a 9to5-job.
The trick about startups is that they can produce huge ROI, but this usually happens when you do something smart, not when you do twice as much as others. When you work twice as much, you earn twice as much maximum, subtract taxes, subtract lower quality, ..
So the net gain from them working late is probably and will only cause long term problems, so if you don't see the product doing insanely great, you should consider running because the equity means nothing then, as profits are determined by profit for normal work times invested time.
If you want to stay, you can either play along, play along for some days when morale is critical, play along on wednesdays, not play along at all. That's a decision we can't make for you.
You could also split your day, work some hours, then leave and live your life, then come in and work until late. But that all depends on you. You define what is right or wrong for you, don't let others dictate it. Getting paid for no work might get hard though.
And if you agree to anything, get in writing for how long that will go, how much you get in return. If not as a contract, then at least as an email. - Keep that mail outside the office or you might not be able to access it one day.
You are doing extra work, basically as an actor who pretends to work, you should get paid more if it's that valuable for the company that you are present. Look up hollywood celebrities to determine the rate for your after-work acting gig. ;-)
And take care of your wife and family, they might not be around one day if you are keep coming home when everyone is asleep.