Seven to eight decades after 1928 is 1998-2008. Female participation in the labor force grew significantly prior to that, though the main impetus was probably the Second World War.
Only 43.3 percent of women worked outside the home in 1970. It'd be some time yet after that before most of them did. The point was that your argument against the washing machine was incorrect. Those 10-15 hours a week were actual gains for the working class. Women didn't jump into the labor force right after that machine was created and sold, after all.
It was an enabling factor but not a causative factor.
Another question: what proportion of homes had washing machines by year starting in 1928? Large proportions of American homes weren’t even electrified in 1928.
