The truth is that there is not one specific timeline that you can follow during your acne treatment.
If your acne is common, you will likely always have good hygiene or continue to use an acne treatment product for the rest of your life until your skin no longer becomes prone to acne, which is generally your later years.
If your acne is cystic, your timeline can range from a few days to a few weeks or months, depending on the specific treatment recommended by your dermatologist.
The most important thing to look out for here is that good hygiene is the key to generally reducing acne.