xiamen layover

Yes, your itinerary is definitely eligible for 24 hour visa free transit and you don't need any kind of visa. The reason is simple. As you can see, the total transit time from your first landing in China, in your case in Qingdao, until your final departure from China, in your case from Xiamen, is less than 24 hours long.

You will print out your flight tickets and have those printouts with you. Also, you will declare at check-in in US that you will travel to HCMC via China using 24 hour visa free transit. After a short check of your tickets, you will be allowed to board the plane. Since you will obviously use MF858 from Los Angeles to Xiamen, and MF8005 from Xiamen to HCMC, you will inform yourself about the luggage policy because it is possible that you will have to collect your luggage at some point and perform a recheck after that. I cannot confirm that, but you should ask about the details, just to be well informed and prepared.

Upon your landing in Qingdao, you will apply for a temporary entry permit at 24 hour visa free transit counter. This permit will be granted to you free of charge because your next flight segment is considered a domestic one, although it will be on the same flight number and by the same aircraft. You will also clear immigration in Qingdao. This is perfectly normal. Upon arrival in Xiamen, you will be able to explore a city for a while and after that you will just return to the airport to continue your visa free journey to HCMC.