Your question is very hard to answer because there are so many different variables How long a course are we talking about - one hour or twenty hours? Is it your first course or tenth course? Obviously the first one takes a lot longer as you learn, practice, your presentation skills, video editing, etc., etc. My advice is don't worry about how much time it takes. Take as much time as you need to produce a very high quality course. Your course will only succeed if you have put in the time and effort required.