Let's get all the facts in 1 post...
In the late afternoon, HKO gave the 2 hours notice that T8 would be hoisted in the early evening, with it eventually being hoisted at around 6pm.
I believe most employees head home at or around this time.

T9 was hoisted at around 11:30pm. While there may be a few workers who are stuck in their office, given the time of the night and that it has been 5.5 hours since T8, I am quite surprised that there are still people out and about.

T10 then followed at around 12:45am. At this time, there really wouldn't be many people about, even for a non-typhoon week night. It has also been almost 7 hours since T8, so it is beyond believe that there are people still trying to get home on the MTR.

Funny enough, in most countries, when a typhoon is coming, people would head home and bunker up. In Hong Kong, during T8, people happily get out of work, and celebrate the no-work-day in style - going yum cha, watching movies, singing karaoke, etc. Guess who's to blame when there's no transport home at the end of the day.