This formula's own materials give this specific, practical tip: save your order confirmation, since your 60-day window is based on your purchase date.
This formula's own materials list this as one of their five tips for best results — worth reading it as a direct, practical instruction rather than routine fine print.
Save your order confirmation email as soon as it arrives, and note your exact purchase date, so you have a clear personal record of when your 60-day guarantee window began.