For teachers starting in the world of pre-recorded lessons and screencasts for teaching, there's no doubt that they will be asking themselves a number of questions such as: how long should the video be?, how detailed should I make it?, what if it's not of a good enough standard? These are all perfectly normal. According to renowned education professor with the Open University, Paul Kirschner, the most important thing is to keep it short and simple. He recently gave an online presentation with ResearchEd on Ten Tips on Emergency Remote Teaching which can be viewed here.
It is also interesting to know that the optimum time for an effective pre-recorded video is up to 6 minutes. Between 6 and 9 minutes engagement begins to drop and after 9 minutes engagement drops considerably. A very interesting article on everything you need to know about screencasts can be found here.