10 hours layover in pek airport

James, there is no 24 hour transit visa. You are actually looking for a temporary entry permit. It is important to use correct terminology to avoid any possible misunderstandings.

So, your itinerary is definitely eligible for 24 hour visa free transit in Beijing and you don't need any kind of visa. You will print out your flight tickets and have those printouts with you. Also, you will declare at check-in in Los Angeles that you will travel to Tokyo via Beijing using 24 hour visa free transit. After a short inspection of your flight tickets, you will be allowed to board the plane.

Upon your arrival in Beijing, you will approach 24 hour visa free transit counter where you will apply for a temporary entry permit to be allowed to exit the airport. If you plan to join a tour (you can find some of them on Beijing layover tours website) you should pick one and also book it in advance and have a confirmation printout with you that you will present to the authorities. With such an application you will practically assure a successful granting of the mentioned temporary entry permit that is always issued under discretion of immigration officials on a day of your arrival in Beijing.