Watching online tutorial videos can become addictive. Keep in mind that you are trying to learn something, not get distracted.

How long you would be able to study depends on the density of the subject and the level of your knowledge about the subject.

Find out the ideal time you can dedicate to learning, and also resting.
Don't try to push yourself and to fill your mind with too much information in one session. Try to learn over multiple days to let the information sink in.

Watch the lesson through once. Then watch it again while following along. You can also follow along from the start.

Take notes. Write down important steps, tips and tricks.

Once you've learned a new skill, try it out for yourself. You will make mistakes. When you do, review your notes and keep going.

You'll learn the most from your own early errors.

Once you've learned something, review it regularly to make sure you don't forget it.

It is not necessary to actively watch a lesson you've already seen. However, it can be useful to have one on in the background so you can tune in and out as needed.