The testimonials mention changes by about week three and by day ninety, two points on very different timelines.
A change by week three is faster than the brand's own 90 to 180 day suggestion. That could be a real early response, an expectation effect or something unrelated, such as a better week of sleep. Day ninety fits the brand's stated window, and it falls after the 60-day guarantee has ended.
Neither tells you what the formula did, because the writers' starting points and other habits are unknown.
Set your own check-ins: a baseline, then week three, day 30, day 60 and day 90. Compare the same ratings each time. If you notice something early, note it but do not rush to conclusions. If nothing has moved by day 60, you still have the option of using the guarantee.