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No — sunscreen prevents new UV damage, it doesn't reverse pigment that's already formed. You need both: sunscreen to stop it getting worse, a pigment-correcting active to fade what's there.

Sun damage tends to be scattered, irregular spots on consistently exposed areas — the face, backs of hands, chest. Melasma is more symmetrical and mask-like, often linked to hormones. Acne marks follow the shape of a healed breakout. See Dark Spots & Pigmentation if yours sounds like either of the latter two.

Yes — retinoids improve both the pigmentation and the texture and fine lines that come from cumulative UV exposure, which makes them one of the more efficient additions if sun damage is your main concern. See Retinol.

Realistically two to four months of consistent use, and progress stalls or reverses if sunscreen isn't worn daily throughout — that's the single biggest reason people feel like it's "not working."