I highly doubt it, but you probably should do it 2 hours to at most a week after photoreading.
The reason I doubt it is because recently I've been remember thoughts, yes THOUGHTS, that I had back in elementary school, and remembering where I had those thoughts.
Even dreams from years and years ago.
I really really doubt that you actually "forget" anything.
If you want to activate it a year from now, you might as well just photoread it again. It only takes a few minutes.
