We are currently working on creating a video to promote the features and functionality of our app.
We would also like to understand what constitutes screencast time, and if the "up to 25% of the time using screencasts" guideline mentioned is mandatory or just a recommendation.
Don't include long screencasts of someone using the application. Up to 25% of the video can use screencasts for demoing features, but the video should be promotional, not instructional.
Screencast is a screengrab of your actual app UI and backoffice. So this type of content shouldn't exceed 25% of the promotional video length.
This is a recommendation towards best practices, so your app looks more intriguing to a potential User and encourages further explorations of the features/benefits.