I would certainly encourage you to find the appropriate professionals to help you through the process both legal and real estate. Without knowing more about the property and it's current condition it is difficult to give you a specific time-frame. If you are paying cash it could go fairly quick, but you will probably want to get some Title Work done which may take some time depending on the status of the title. You should get legal council, if you don't have already, and get in touch with the agent. You should also understand if there are any zoning/easements that place restrictions on the property and that might prohibit the placement of a manufactured home.
Hope that helps, keep us updated as you contact the agent.