They don't have to take a shower on New Year's Day.
I guess it could be change to count whether if the number of days since Jan 1, 1970 up to today has been odd or even...
Probably since otherwise you’d just need a calendar or somehow know the date which most people do without custom code
Even if the decision was merely day-of-week based, that doesn't buy the key characteristic the author values (I assume): the kids will accept the Algorithm's ruling