How long do prescription acne medications like aczone have to stay on your face to be effective?

Every morning when I wake up, I wash my face and put on my aczone. Then I go to the gym and sweat it off for a few hours, and then go home, shower and wash face and reapply. It says once a day but I figured since it isn't on very long, I should reapply. Will this harm my results? Should I only apply it later in the day? Or is what I am doing OK ? I've only been using it for 5 weeks and my skin is still purging somewhat. I also use another prescription cream at night.

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