

2 Adults traveling from UK to Japan through Shenzhen with 13h and 19h layover-leaving airport??
My partner and I have a 19h one way and a 13h the other way layover in Shenzhen on the way to japan. We are both British citizens and I also have an American passport. I’m quite confused about the concept of 24/72/144h visa-free. One place told me 144, another told me 24 and another told me not at all! Whichever it is (unless it’s the not at all), considering it is visa-free, do we just show up with the up to date passports and tickets and nothing else, or do we have to apply somehow? Something online was talking about needing paperwork from our Chinese embassy? And, how does it work with leaving the airport to say, get some street food?
Finally, with the covid tests, now that they’ve reduced it to just antigen tests, what proof do we need? If we do the basic antigen tests at home(not the ones that come with paperwork) and can check a box saying they were negative, is that enough? Or do we need ones with actual paperwork?