It really is an individual thing and often time-dependent. As it takes time to alter the good to bad bacteria count in your gut, once you are past the 8-week point then you have likely altered the microbiome of your gut.
So you should be noticing measurable effects on your well-being. If you were to stop taking it, you might feel some lasting effects for a period, but depending on your lifestyle, eating habits, hormonal fluctuations, and stress levels, you could also notice a return of symptoms that had stopped while you were taking Provitalize.