Wait a minute...
15 years ago
General
What the hell kind of smelting plant is open in the middle of the night like that? And who needs an entire transport truck full of liquid nitrogen? And why would the highway lead directly into a dimly lit, densely populated workplace full of molten steel?
FA+

lol
They'll find you!
The smelting plant was open late at night due to a rush contract from a supplier who had a major order placed from a large overseas company for a massive construction project.
I have not seen the movie in a while but I thought I saw them take a turn off the highway to a smaller road that led to the smelting plant. They did bust through a gate as well to go into the factory.
<--Killjoy!
LN2 is just another cargo delivered by tanker truck. It is often delivered in bulk at night or on weekends to customers because of the awkwardness of driving a tractor-trailer full of hazardous material through the parking lot full of employee cars.
You can't let furnaces go out. They have to run forever after you start them up. If they shut down, steel (or whatever you're making) will solidify into the mechanism, which deforms the shape so it can't be started again.
And if you work at a national lab or research university, you see truck fulls of liquid nitrogen come by every day for delivery, and sometimes at odd hours for various reasons.
also heres a vid ya should check
http://www.youtube.com/watch?v=bBBw9E2Q_aY&feature=BF&list=SL&index=20
also about the questions, its hollywood dude, they build suspense without caring how is it possible
...or convenience... ¬.¬
They have around the clock shifts.