This site states this specific figure directly in its own customer-feedback stats: 2-4 weeks to notice a difference.
Rather than a vague "give it time" instruction, this site names a specific range — 2-4 weeks — worth planning your own evaluation around that stated window rather than judging within the first few days.
Many products in this category promise instant results — worth reading this site's own specific, multi-week window, connected directly to its 60-day guarantee framing, as a more honest baseline than a manufactured overnight-results claim would be.