Help, do I need a transitvisa when going through to destinations of China?

I am going from Phnom Penh, Cambodia to Copenhagen, Denmark. I have to stops in China before my final destination which is from Shenzhen to Chengdu. My trip is estimated to be be 23h30m in total. So, what if some of my flights are delayed or something? Can I still do the 24-hour rule? My e-ticket says that a chinese visa perhaps is to be required from Chengdu to Copenhagen which I find a bit strange since I will not pass my 24-hour rule?

Thank you so much for your great help - you guys do an amazing job! From Anja