Not to sure about transit times

Hi please can you help me as I am visiting my girlfriend who teaches in Guangzhou and I want to know if the flights I have booked are correct and qualify for the 72 hour transit visa.

I fly from siem reap at 9pm 30th June to Guangzhou and land Saturday 1st July at 1.20am

I have a flight booked Tuesday 4th July at 2.50am from Guangzhou to Bangkok where I am getting a flight onwards to London at lunch time.

I am traveling on a UK British passport
Please help would be very much appreciated 😊