Why can’t it take place over multiple days? You see the days go past?
It can and does. Unless you have a better explanation as to why the skybox goes from day, to night, back to day, then night again over the course of the game. Something other than “it was an oversight.”
It does? I only remember it going dark once.
I’m wondering if he’s thinking about Xen…in which case, the skybox don’t count. 
No, I’m not.
Then, what are you referring to? You shoot the rocket at night in On a Rail, it’s daytime when you awaken in the garbage compactor and get to the surface in Surface Tension, ten it’s still day in Forget About Freeman, and you go back underground in Lambda Core. Where is this second night?
He slept for 2 days in the garbage.