I got to say, I traded in US for many years, there was no such...

I got to say, I traded in US for many years, there was no such concept. Only "Circuit breakers", introduced after Black Monday 1987 (DOW fell 22.5% that day, never seen before or since), when if market crashed x%, then it would all shut down for a breather, a larger %age, then longer still . We saw this in China recently,...they actually removed these "circuit breakers".....
I agree with that. If there's something really bad is happening, and you want out, you can't.
It's to avoid a further panic, obviously, but when it re-opens they panic and sell anyway.
Also, most Announcements and Forward Guidance and Analyst questions etc....and are made after Mkt Close..like earnings, say.....in fact...always.

They also introduced about 15 years ago, Extended Trading Hours, so after about 4:30 pm, the Extended Hours session began...less liquid, the players have gone home, but you can trade....but if there's an Earnings Ann, say, from IBM, announcing the 16th successive Qtr of declining revenues (at 15 now..), it's IMMEDIATELY reflected in Extended Hrs Trading....and that's where it will roughly open the next morning. You read about this all the time.
"ABC" company traded down $2.65c after announcing disappointing Earnings today" etc....
In plain English, a co. ANN should not be a reason to stop trading.