Ms. Osborne notes that in Edwardian London adulterous affairs tended to be conducted between the hours of five and seven (known as a “cinq à sept”) because it took women lots of time in those days to unbutton and unlace their layers of corsets, chemises and underskirts, let alone relace and rebutton them up afterward, so lovers scheduled their visits for just after tea when “ladies were undressing in order to exchange their afternoon clothes for their evening ones.”
Source: wiktionary