Maybe 3-4 hours. Maybe less.
Buying a mobile or manufactured home is like buying a car. In many places--for example, where I am, in Virginia--you go down to the Department of Motor Vehciles and get it titled or retitled.
Last summer, I sold a manufactured home. The buyer and I went down to the DMV and in 3 hours it was his. It would have been faster, but one of the computer systems was down.
Now, that's assuming a couple of things. First, that you've already been approved by the park management, if the home is in a park. The home I sold was in a community that required both a background check and credit check. That typically took 48 hours. So if there's an approval process from the park, you have to build that in.
It's also assuming that the person you're buying from has clear title, and that you're dealing with all the sellers.
The answer below suggests a home inspection. That's good advice. If that hasn't been done yet, that can be handled in a few days.
But to answer your specific question--you posted your question about 10 am California time. It's possible you can move in and eat dinner there today.
Hope that helps.