Ho Chi Minh - Guangzhou - Kathmandu

You definitely enjoy the 24-hour visa-free transit and can leave the airport for sightseeing as long as you get a 24-hour visa-free entry permit at the border inspection counter which is easy to get.

The first and the most important detail is that your itinerary is definitely eligible for 24 hour visa free transit and you do not need any kind of visa. Also, you are advised to use correct terminology because it is 24 hour visa free transit and not 24 hour visa. There is no visa at all.

Also, you should be aware that the basic rule of 24 hour visa free transit says that the citizens of all countries have right to travel through China visa free, but to remain in the transit area of the airport. The main detail here that confuses many is that they mix up the right to travel on visa free transit and the possibility to exit the airport and to explore the city. These are two different things. 24 hour visa free transit means that you will transit through China visa free and stay in the transit area. If you want to exit the airport, you will apply at the transit counter a temporary entry permit by presenting your flight tickets. This permit is not a passenger's right, but you can treat it more like a bonus that is granted in cases where airport authorities see a justified reason to allow a person to exit the airport. Airport authorities have relaxed the criteria for the issuing of the permit and this has brought many in the situation to think that the permit is the same thing as 24 hour visa free transit status.

So, you will apply at the transit counter for a temporary entry permit hoping that you will be granted that bonus. It can be issued to your or not, depends at purely discretionary decision of the airport authorities on a day. Since your layover is a longer one, I would say that your chances are fine, but as I said, you really never know.