This mask is designed as an occasional intensive step — think of it as a weekly or bi-weekly treatment rather than a daily product. The source guidance suggests using it "especially before an event, after travel, or during periods when the skin looks dull and drawn." A practical rhythm for most people is once a week, or twice if the under-eye area feels particularly dehydrated or puffy (for example, after a long flight or a string of late nights).
In a routine, apply it after cleansing and any toner or essence, but before your regular eye cream and moisturiser. The mask delivers a concentrated dose of hydrating and barrier-supporting ingredients (squalene from shark oil, polysaccharides from kelp, panthenol), so following with your usual eye cream helps seal in that moisture. It does not replace a daily eye cream; the source explicitly states it "works best as an occasional intensive step alongside a gentle cleanser and a basic eye cream, not as a replacement for them."
Because the format is 10 ml, you'll get several applications per tube. Use a pea-sized amount for both eyes — the skin there is thin and absorbs product quickly. If you notice any irritation, scale back frequency or pause use.