My first piece of advise is 'don't should on yourself'. No need to apply a multitude of rules to photoreading.
Try activating a book that you haven't photoread and compare that with one of the same thickness and same level of interest that you have photoread. I think like many others you will notice a difference. 
Photoreading again... is a matter of choice not necessity. I for one will photoread a book again if I haven't activated it for a period of time... that 2 to 3 minutes spent photoreadings refreshed the mind and makes activation easier... helps me to hone in on the information I am seeking in a matter of minutes.
If you're direct learning the thats when the photoreading step counts, you never actually need to activate any of the book from the direct learning pile (though one or 2 might inspire you to do so for some reason).
Maximum is what you are comfortable with, overnight break is recommended and 20 minutes as a minimum before activation. These ideals are not set in stone. Again if a week has passed I find it easier just to photoread it again, quick, before activating immediately.
You may consider photoreading again if you are doing multiple activation passes. That is your choice.
Longer isn't necessarily better. The longer you look at the page the more likely the conscious mind tries to take over the task. If you can turn the pages faster than one per second and hold the steady rhythm then go for it.
It's kind of difficult to write one book to suit everyones learning style. That's where the forum comes in.
Alex
