I just graduated in China and got a warning for one day overstay cos my flight delayed.

Eli, you cannot fight the immigration authorities of the Philippines because they will do exactly as they want. In reality by far the best situation is to accept a flight via Shenzhen because it allows 24 hour visa free transit. Your information that Shenzhen does not allow 24 hour visa free transit is outdated.

So, just accept a flight via Shenzhen, but have in mind that your flight out of Shenzhen has to depart within 24 hours after the scheduled landing. So, there will be no problems if you take this option because you will be perfectly within the Chinese transit rules. There is another thing and here I strongly discourage you to try to exit Shenzhen airport regardless of the length of your Shenzhen layover. I hope you will understand me... You were warned by the Chinese authorities because of the overstay and now you will be departed from the Philippines. So, remain airside and just wait for your flight out of Shenzhen to your following destination. I wish you the best of luck and hope you will finally reach your home.