I've done open houses Sundays, Saturdays, and weekdays.
The weekday ones in our market went horrible. Usually a neighbor who wants decorating ideas because "our house is the identical floor plan!" or "i just listed my house last night with somebody else" type of neighbor...that's if anyone showed up at all.
Saturday mornings you get people who were driving by signs mostly - if you're in an area with a lot of yard sales you stand a decent chance. These are mostly impulsive people though just curious or "looking for a friend".
But Sundays come people who know that a lot of houses are open, they researched them online, they're talking about another listing they saw...
I don't know who picked Sundays originally and how it stuck, but if they had results like mine, that might be why
