The Gemara says that when "God called the light day, and the darkness God called night", it doesn't mean God named them that, it means God called them like you call your friend. So God is like "Hey, Light!" And Light says "Hineni."

"Light," says God, "I need you to Do Stuff in the day. Where's that other guy? Hey, Darkness! Where are you?" Darkness pops in and says "Hineni!" "Darkness," says God, "I need you to Do Stuff in the night. You guys got that?"

Darkness and Light look at each other and say "Uh... Sure, no problem, you're the boss. Just one thing - what's 'day' and what's 'night'?"

"How should I know?" God says. "I just invented time this morning, and then I had to go back and implement it retroactively so there would *be* a morning I could invent it in."

"All I know about it so far is that it's not linear, but it will *seem* linear to humans when I get around to inventing those. I'm busy, I'm delegating this to you guys. You figure it out."

God heads out to separate the waters from the waters. Light and Darkness stand there for a minute, and then start trying to figure it out. After a while they decide that since the only solid instruction they have is to Do Stuff, they'll both just Do Stuff all the time.

They'll leave it up to some other construct, like Position In Physical Space to determine which of them appears to be doing *more* stuff to the humans at any particular point in time, which isn't linear anyway and doesn't actually have points really.

And that is why "or", light, can mean evening or day, depending on how you think about it.