72 hours visa question

Hi, im not sure if i can buy this ticket cause im confused about my situation in this case. On the first flight i have just a 2hour transit in shangai onmy way to bangkok. I think i should be ok with it. But on flight 2 and 3 (bangkok- beijing / beijing- tokyo) My plan is to stay 72 hours in beijing but: i have transit 2 hours in shangai . Does it affect my 72 hours in beijing or my entry is at shangai? and also my flight arrives beijing at 11:45 on the 25th and next one is 4:40pm on the 28th. Its technically almost 77 hours but since i need to be 3 hours earlier at ariport and stuff .. would it be ok if i just go back to the airport at 12 to be ok with the 72 hours and wait for my flight?
Thanks.. here is write the route so you can tell me

FLIGHT #1

Take-off Thu 4:50p KIX Osaka, Japan
Landing Thu 6:20p PVG Shanghai, SH, China

Change planes PVG Shanghai, SH, China
2h 35m

Take-off Thu 8:55p PVG Shanghai, SH, China
Landing Fri 12:35a BKK Bangkok, Thailand

FLIGHT #2

Mon, Mar 25 BKK to PEK – 1 stop 8h 50m


Take-off Mon 1:55a BKK Bangkok, Thailand
Landing Mon 7:00a PVG Shanghai, SH, China

Change planes PVG Shanghai, SH, China 2h 15m

Take-off Mon 9:15a PVG Shanghai, SH, China
Landing Mon 11:45a PEK Beijing, BJ, China

FLIGHT #3
Thu, Mar 28 PEK to HND – nonstop 3h 20m

Take-off Thu 4:40p PEK Beijing, BJ, China
Landing Thu 9:00p HND Tokyo, Japan