How long should an instructional video be?

Came across an article titled "How long should your next video be?", which I have found useful. Drawing on large-scale research on viewer engagement, the writer highlights a few findings, two of which have come across as most interesting to me:

1. Loads of engagement within the first two minutes, which drops off significantly after the second minute.
2. However, from the sixth minute onward until the 12th minute, engagement stays more or less constant.

How should I interpret this? I guess the message is that for those viewers who have struggled, or persevered, to use a more positive term, up to the 6th minute, they're now motivated enough to want to learn more about the content.

And perhaps the implication for teachers in terms of producing longer instructional videos is that they should pay sufficient attention to how to engage viewers for the few minutes after the second minute.

https://wistia.com/learn/marketing/optimal-video-length