The key phrase is from the purchase date.
The guarantee is 60 days from purchase, per the brand. The page also advises getting terms in writing, because the exact refund start date and fees are not stated.
The clock starts when you buy, not when the parcel arrives. With a 90- or 180-day supply, much of the product will be used after the window closes. Judge early and ask support in writing how they count the 60 days.