24 hours transit russia with separate tickets

Yes, you are allowed to have more than one stop within mainland China under 24 hour visa free transit scheme and you are also allowed to travel on separate tickets and on unrelated airlines.

I can see that you understand the concept, but you should be absolutely certain that the entire transit time you will spend in mainland China will be under 24 hours. Many passengers tend not to count the time spent during the flight between two mainland Chinese cities, but this time, spent in the air also contribute to the overall transit time. It is always the best to calculate your entire transit time starting from your first scheduled arrival, in your case Beijing, until the last scheduled departure, in your case Kunming. If that total time is shorter than 24 hours, you are good to go.

I advise you to print out your flight tickets in order to speed up the entire process. Also, you should have in mind that the first thing that you should do upon landing in Beijing is to approach 24/144 transit counter where you will apply for a temporary entry permit by presenting your flight tickets. This application is free of any charge. After a short check, your permit will be granted and you will proceed to the immigration, collect your luggage and perform new check-in for your flight to Kunming and eventually to HCMC.

Your flight Beijing to Kunming will be a domestic one and upon landing in Kunming you will cross the exit immigration and board the plane for HCMC. Basically this is it. Have a nice journey.

Good to know, thank you!