The actual amount of time a student spends watching your videos is what will count toward your total minutes watched. For example, if a student watches your 10-minute video in 2X speed, this would count as 5 minutes watched. If a student watches your 10-minute video in 0.5X speed, this would count as 20 minutes watched.
It might be tempting to teach longer classes to recoup for this difference, but in practice, it’s generally better to always create high-quality classes that are appropriate in length for the content being taught. In other words, making a class longer just for the sake of it may actually lower the quality of your class and reduce student engagement, resulting in fewer minutes watched. For more information on recommendations for class length, refer to the article How long should a class be?.