You got it right you spend about 4 seconds per page superreading you dip for one or 2 sentences or a paragraph. The move on. Have an idea what you are looking for during your 20 minute pass ... the characters, the plot, the theme. Be clear what you want to know from the book and ask yourself questions in relation to it. Remember the who, what, why, when, where and how questions. Write them down.
If you're tired definately keep the activation short and mind map anything that comes up during the activation.
Alex