Probably not fired. But the interior motion sensor alarms go on automatically at 7pm, which would probably alert the security guards that roam the campus.
When I first started, I came in too early once and set off the alarms. People were nice about it, but I was super embarrassed because I was a n00b.
Personally I strongly prefer no fixed working hours. If you want to work at night, so that you can do things when it’s light out (especially in winter), and you still get the expected results, what’s wrong with that?
I worked at a place like that once. When I was hired I was told I could make my own hours. I prefer to work early mornings, so some days I came in long before anyone else. A couple of times around 3am. But I always worked at least eight hours, and often more.
In my exit interview, my supervisor was rabid about how I wasn't a good fit because I "come and go as [you] please." She was so full of crap about other allegations against me that I didn't even have a chance to bring up that making my own hours was part of my employment deal.