The page's own FAQ asks why the guarantee is shorter than the suggested use period, which is to its credit.
It acknowledges two numbers that do not match: 60 days of money-back cover and 90 to 180 days to evaluate properly. The footer repeats the point, telling readers to track their purchase date if they want the option of a refund.
We do not know the reason behind the choice and will not guess. What matters is the effect on you.
Treat the guarantee as a 60-day trial of whether Honeyfil suits you, not of whether it works over six months. Decide ahead of time what you will accept as a good sign at 60 days, like easier routine or steadier afternoons, and keep notes. If you continue past day 60, do so knowing the refund option has ended.