You can activate any of those books you read at any time in the future. However, if that time frame is longer than the next day or two, I would consider PRing the book again before activation (just to refresh the neural pathways), but I wouldn't wait another sleep cycle. I would consider waiting for the recommended minimum 20 minutes before activation though.
This whole process of re-PRing the book and waiting before activation would only take about 30 minutes, so the time thing is negligable and I think you would get better activation results this way rather than simply trying to activate something you PR a week ago.
Gregory
