Take a five minute break after 20 to 30 minutes anyway, then take a 10 to 15 minute break after the next 20 to 30 minutes.
For activation I would suggest that you focus on say the characters for then setting, plot location, theme, Symbolism, Philosophy, Imagry etc. If you superread and dip with those things in mind you'll probably be able to finish the book in a lot less time. You could probably find the answers to those questions in an hour. Once you have them you have the option of doing a rapid read. You'll probably spend a lot less time on it by first superreading and dipping for an hour discovering those details.
My questions article explains what to look for in the way of theme, symbolism etc. If you haven't got a copy feel free to email me for one. 
Alex
