As of my knowledge cutoff in September 2021, melatonin diffusers were not a commonly available product, and research regarding their specific duration of effect may be limited. Melatonin is a hormone naturally produced by the body to regulate sleep-wake cycles. It is commonly used as a supplement to help with sleep disorders or jet lag.
The duration of the effects of melatonin can vary depending on several factors, including the individual's metabolism, the dosage, and the form of administration. In general, the effects of melatonin typically begin within 30 minutes to an hour after ingestion and can last for several hours. The exact duration may differ between individuals.
If you are specifically referring to a melatonin diffuser, it would be helpful to consult the product instructions or reach out to the manufacturer for more accurate information on the duration of effect. Keep in mind that the availability of new products and research beyond my knowledge cutoff might have changed, so it's always best to consult up-to-date and reliable sources.