II skin with VI hyperpigmentation? When will it fade?

I have PCOS & Hypothyroidism which might be the reason for my hyperpigmentation. I was advised to use hydroquinone 4% since it's the fastest safest solution for this problem. How long will it take for my VI areas to return to my original color? & if you have a better solution? Also will losing weight help or not? My original color is II but the dark areas in my body which are my elbows armpits bikini/backside/inner thigh area my knees & toes are VI which is a very big difference than my color.

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