What is the certain time can i be exposed to the sun when i used hydroquinon cream on my face to fade dark spot? should i forever hide from the sun?

Avoid Sunlight: Sun spots, melasma and other causes of skin pigmentation can sometimes be lightened with bleaching creams like hydroquinone (hq). It is important to note that any exposure to sunlight works against you. Shading the skin with a wide-brimmed hat and sunscreen (spf 30+) is the best way to help the hq work for you. You will always have to be mindful of sunlight to avoid re-pigmentation.

HQ & sun exposure : When using hydroquinone products, you should not intentionally expose the treated area(s) to sun. This means no sun bathing or working / playing in the sun without uv protection ie spf 30 sunscreen, wide brim hat etc. Intentional, unprotected sun exposure defeats the purpose of lightening dark spots that typically darken upon sun/ uv exposure.