Travel economics might affect how long you want your China business trip to be. If you are having major problems with a million dollar project, you probably will not object to staying in a hotel for a week or more. You may be able to resolve the problem in a day or so but if it was that simple, you probably would not be making the trip. If the problem does turn out to be easier to correct than first anticipated, you can always use the extra days to visit a few other factories.
Since your flight is the single most expensive cost factor of your trip, it can make good economic sense to stay a few extra days for additional supplier meetings.
You might purposefully plan the trip be close to the two main Trade Fair seasons. These are in April and October. This presents an opportunity to meet many new suppliers by attending one or two Trade Fairs in China and meeting with your current supplier at their factory. If you do this, plan to be in China for between 2 ½ -3 weeks. This is the typical amount of time seasoned importers plan for during the Trade Fair season.
I have also met business travelers who arrived on Monday morning, have their first meeting at noon, and leave by Tuesday night. Seems a little senseless to me that they spend more time flying than they do at the factories. Somewhere there might be a little financial sense in this but it puts a lot of stress on your body and does not allow you to do a professional job with the Chinese companies.
A balanced philosophy is to make the business trip as short as possible and as long as necessary to achieve your goals.