What is the recommended length of time for using differin (adapalene) 0.1% gel to clear up acne scars?

Scars are permanent! Differin (adapalene) gel reduces the tendency for your skin to have new acne outbreaks and additional scarring, but will not remove or eliminate scarring that is already present. Chemical peel, dermabrasion, or laser resurfacing can help to reduce scarring, but no technique, laser, cream, and surgeon can completely remove or eliminate scars. Improvement is definitely possible, however.
3-4 months . If you were prescribed differin, (adapalene) your scars aren't very bad. Differin (adapalene) is good for very mild acne and it produces less photosensitivity than other retinoids. In general it takes most retinoids 3-4 months to peel the skin enough to remove the discoloration from superficial acne scars and rebuild collagen. Should use spf of >30 in daytime all year long to keep those scars from darkening or reappearin.