What to do when the organizers close the submission portal earlier than what was announced? I was submitting the camera-ready version of my paper to a conference in China, and its deadline was by the end of Sept. 7th based on Pacific daylight time. But, they closed the submission portal at 16:00 (PT) Sept. 7th. 

I already contacted the program chairs (which are Professors of Chinese Universities), but I have not heard anything back from them. I imagined they have closed the webpage (maybe by automatic settings) according to their local time in China which is more than half a day ahead of PT. But the conference website (keydates) clearly says that all the deadlines are at 11:59PM Pacific Daylight Time.

Update: After exchanging a couple of emails they noticed it was a technical problem from the web service they were using for submission management. They solved it eventually and now everyone is happy! :D

So, what can I do instead of giving up on my paper?
Expecting them to be checking their emails on a weekend is a bit presumptuous. It is Monday now in China, give them a chance to have a coffee, get through some admin, and then deal with their inbox. You may not be the only one emailing to complain.