How long should I wait after active acne to get needling (dermaroller) for acne scarring?

I have been using tretinoin 0.1% for 3 weeks and my acne is clearing up. I have no cystic or inflamed pimples, just a few small bumps. I have a lot of red marks and scars from recent pimples. How soon can I start needling treatments for the scarring? Do I have to wait until the red marks heal, leaving behind skin-colored pitted scars? or can I start right away?

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