As stated in the first question of the FAQs, you can start to use this method instantly, but learning times may differ at the beginning, depending on the subject.

This is predominantly due to how used your mind is to learning that subject.

It's also worth noting that you may 'feel' it is slower to learn using this method. This phenomenon is an illusion caused by you spending more mental effort than before, making time seem to go by differently than usual.