I figured it was because the staff are going to be the only ones working late at night. Makes sense that the spooky stuff would only be noticed near where they're working.
There's also the possibility of security guards seeing weird stuff, but I'd imagine they'd keep their mouths shut to...
Interesting first chapter, looking forward to how this develops.
Though there was one odd translation choice- cents instead of yen. I get that the conversion rate was very different back in the Taisho era, but localizing currency always stands out to me.