This site states this directly, as one of its five tips: give it several weeks — most people don't judge results until at least three to four weeks in.
Rather than a vague "be patient" instruction, this site names a specific range — three to four weeks — worth planning your own evaluation around that stated window rather than judging within the first few days.
Many products in this category promise a specific, short timeline before results — worth reading this site's own specific, multi-week window as a more honest baseline than a manufactured overnight-results claim would be.