24 hours transit visa

If Chengdu is the only landing within mainland China, you will be definitely covered by 24 hour visa free transit and you do not need any kind of visa. In other words, there is no 24 hour transit visa, but 24 hour visa free transit. Now, if you want to exit the airport and I understand it because you have 20 hours of layover, you will approach transit counter immediately upon your landing in Chengdu where you will apply for a temporary entry permit to be allowed to exit the airport. This application is for free and here you will present your onward flight ticket as well your hotel booking confirmation, preferably by presenting it in hard copy (as a printout). You have to be aware that temporary entry permit is issued based on a discretionary decision of the airport authorities on the day of your transit there. However, I do not doubt that you will be granted a permit based on the length of your layover and also by your presenting of a hotel reservation. I would say that your chances to be granted a permit are almost certain.

As far as the hotel is concerned, there is at least one at the airport that is located within a walking distance from several terminals, but I am not exactly certain if this hotel is located airside or not. I would say that it is not located airside, but outside the transit zone. However, the hotel is there. Now, you will decide whether you will book that airport located hotel or one in the city.