Mercuzio,
How much time you need for activation depends on your purpose of the book you are PhotoReading. What do you want to get out of the book? It generally takes about one third of the time you would normally need to read a book. If you are uncertain about activation, try the five day test as Paul suggests in the program. It's on page 77 in your PhotoReading book.
Also try all of the activation techniques if one specific technique isn't working for you. Superreading and dipping, skittering, or alternatively Rapid Reading.
Don't try to comprehend all the material in the book in just one pass. Do multiple activation steps and stick with it until the material gels with you. Divide the book up into chapters and activate each chapter seperately. Make a mindmap of each chapter, and once you've covered all of the chapters you want to get the information from, create one big mindmap that covers the whole book. Reflect on what you've learned, and you will see results for sure.
When you are activating with a clear purpose, look for ideas and concepts. Some words will seem more important to you than others. Once that happens, you can dip in and read the information at a pace that is comfortable for you. The words pop out because you have PhotoRead them earlier, and because your purpose is related to those words.
I hope that explains the process a bit more for you.