Which one is easier to develop and work with (which saves the most time)? Which one would you go for? The name of the API represents its true purpose in this case by the way, createOrUpdate creates or updates the passed in meeting and create just creates the meeting. I will be the only one working on this project for now, although obviously, I would like others to work on it with me eventually.
If the function is doing input validation, it might be cleaner to have a single code path for both creation and update. Especially if you eventually assemble an SQL statement that is INSERT OR UPDATE.