Question on visa for transfer

Hello sir. I have plan to go on a vacation to Germany. But I'm confused about Chinese entry permit because I have transfers.
My flight schedule is as follows.:

When departuring from my country, South Korea:
30th Sep.
08:50am South Korea (Incheon/Seoul) - departure
11:35am China (Shenzhen) - arrival*

17:15pm China (Shenzhen) - departure*
21:10pm Singapore - arrival

23:55pm Singapore - departure
1st Oct.
06:45am Germany (Frankfurt) - arrival

When departuring from Germany:
7th Oct.
22:00pm Germany (Frankfurt) - departure
8th Oct.
16:25pm Singapore - arrival

9th Oct.
07:00am Singapore - departure
10:50am China (Shenzhen) - arrival*

14:00pm China (Shenzhen) - departure*
16:25pm China (Shanghai) - arrival*

10th Oct.
08:30am China (Shanghai) - departure*
11:10am South Korea - arrival

I will stay within 24hours in China for the transfers but I'd like to make sure if I need Chinese visa.