No idea if this is a new rule or just a nasty Thai/Chinese immigration officer.
My 90 days reporting was due on the 31 May. I called at Bangkok immigration 8 days before the due date and they refused to do the reporting saying it was too early though I explained to them I was going up country on business the following day and would not be back in Bangkok until the end of the month.
The immigration officer told me what I knew that there was 7 day period either side of the due date.
My flight from Chang Rai arrived too late for my reporting on the 31 but got to immigration on the 1 June to only to be fined 2,000 Baht for being a day late. They also made me wait for over an hour whilst they filled in 5 books and stamped my passport with a nasty stamp to say I had failed to report on time.
I questioned her about the 7 days period either side of the due date and she said and asked why there was no warning signs on this new rule the only reply I had was "no more, must do on the date" I also asked to see her supervisor who also confirmed the 7 day rule has been cancelled.