30 days visa

Hi my parents are coming with me to Japan on Sunday (august 9) and was granted a 30 days visiting-family visa. When I booked their flights back to manila i overlooked that dates since July has 31st i thought August has 30 days only so i booked their for september 8 which makes it 31 days in Japan.. I tried rebooking their flights but the flights are fully booked already... would their be any conflict with overstaying for a day???
Please help... thanks.

Overstay is overstay. Not worth the risk I think, as they could be banned from future entry to Japan for some years for this.

Yes- even that one day would cause all kinds of trouble- interrogations, possible detention, probably bans of up to 10 years. I am afraid you have to change the dates if the flight- Japan is not at all lenient or flexible about things like this.

how do we start counting the days???
If my parents are arriving on the 9 of August when does it ends???