This is the mistake almost everyone makes. Once the sheet starts to dry, it begins drawing moisture back off your skin. Leaving one on for an hour is worse than ten minutes, not better.
Where it goes in the routine
After cleansing and toner, before moisturiser. The mask is a treatment step; you still need something on top to seal it in.
Do not rinse afterwards
Pat the remaining essence into your skin. Then use what is left in the packet on your neck, shoulders and the backs of your hands — that is a third of the product most people throw away.
How often
Two or three times a week is plenty. Daily masking is a marketing idea, not a dermatological one.
A tip for hot weather
Chill the packet in the fridge for twenty minutes first. It reduces puffiness and is far more pleasant in an Indian summer.