I have what I think is a novel idea for a mobile app, and I would like to develop it but having a day job this could take a year or two or three. Instead of starting developing now I am considering filing a patent, my thinking being that once patent is filed I could develop the app at my leisure. I would file the patent myself and it didn't work out I would not be heartbroken. Does this make any kind of sense?
Eric, yes it does make sense. Have you continued to develop the application or work on pursuing patent protection since you posted this question?
You do not need to have a full working application in order to file a patent application. You could file a patent application while you are in the early parts of the development stage as long as you have conceived of how to make and use the invention. Conception is complete when the idea is clearly defined in your mind and only "ordinary skill in the art" would be necessary to reduce the invention to practice, e.g., write the application.
If you are at that stage, you should consider performing a patentability search to see what else is out there and make sure that your invention is novel and non-obvious. If the results of the patentability search are positive, then you can consider filing a provisional patent application or a non-provisional patent application.
Because you are talking about software, there also may be considerations related to patent eligible subject matter. Recently, courts and the patent office have clamped down on certain software-related patent applications for reciting claims that are too "abstract."
Try reaching out to a patent attorney or agent.