In my experince, 90 minutes is a good target to aim for when it comes to the length of your course.
This can be made up of 30 lessons (videos) which are 3 minutes long.
This can be laid out as 6 sections with 5 lessons in each section.
It can take up to 1 hour to create a 3 minute video which will include
- scripting the lesson content
- creating some slides
- some practice
- editing your video
You will get faster the more you do it.