Writing does not have to be a career thing, but one can spend one hour on it a day or two or three hours. A session of writing sounds to me like I have accomplished something within a period of time. A session doesn’t have to be a rigid two or three period every day. It’s a session of writing, even once a week, but for every week, not a one-off. This keeps one going.
I think one can be a writer with a little background in some subject or occupation and use that experience and knowledge to approach publishers for assignments and work or submit material that may may publish one-off. One can build up a file of pieces of work in one subject. At the moment, mine is simply reading and thinking about the Bible, which has led to devotional writing.