How Many Hours Should a Startup Employee Work?

As many as agreed on during the signing.

In my case, the company said it was a regular 8-hour day but I was expected to put in time during 'emergencies'. I agreed, and for the most part, that's how it went.

Occasionally they would schedule time on a Saturday, but they almost always gave me time off to compensate. When they didn't, something else was done.

And occasionally, I would put in a little extra time to finish off something I was working on.

On the other hand, other employees have put in massive overtime and generally worked themselves into quitting. Management put pressure on them to do so, but didn't force them. (I'm proof there wasn't force, since I'm still here.)

The key to working at a startup is understanding that they need flexibility first and foremost. Their problems are going to happen at odd times and there won't be many people to fix them. Of course, as I noted above, the company has to be flexible back, or it doesn't work.

I work at a start up and I treat my job like a 9-5. It depends on what you do during those hours that matter.