I had no idea there were people that used midnight incorrectly on purpose seeing as pretty much all notations for time do agree.
12:00 am standing for ante meridiem (before midday) so clearly it belongs to the noon that comes after it.
And on a 24-hour clock it is even clearer, as the 24-hours clock tends to be, that the day starts at 00:00.
And yeah, I understand it uses GMT, as any international website or community should. And now also understand that it is meant to say it starts and ends at midnight of the first day of each month but is just clumsily written.