Question about HL. How long did the Resonance Cascade actually last?

[Milk Queen]

This is something I'm curious about. Ignoring the whole speedrun joke that Gordon Freeman spedran the entire thing; how long did it actually take for him to get from the beginning to the end. Was it one day? Did it take a course of a few days? How long did it really take Gordon Freeman to get through Black Mesa and to the final boss and accept the Freemans offer? I doubt I'll get a true answer, but I'm very curious to see what some of you will say. I personally think it took him at least a whole day if not two days. But for fun I also like to think Gordon Bhopped his way to the end in under an hours. So what do you guys think?

[KirbychuHRD]

You can see the passage of time by observing the skybox whenever you make it to the surface.

The game starts at about 9am, by the time you get your first view of the surface at the end of We've Got Hostiles it's sunset, it's the middle of the night by the end of On a Rail, just after sunrise by the end of Apprehension, then daylight for all of Residue Processing, Questionable Ethics and Surface Tension, and by the time you make it to the Lambda Complex at the end of Forget About Freeman it's sunset again. It's not really possible to know how long Freeman was in Xen, but if you accept Opposing Force as canon then we know from the chapter "The Package" that the Black Ops plant a nuke in Black Mesa early the next morning and it detonated a few hours later.

So if we assume the nuke went off at around the same time Gordon killed the Nihilanth, the full story would have taken just about 2 days in-universe.