on mondays

on monday

on mondays,

on mondays and

on mondays &

b(?:on|in)s+(?:weeknights?|weekends?|weekdays?|mornings?|afternoons?|nights?|evenings?|mondays?|tuesdays|wednesdays?|thursdays?|fridays?|saturdays?|sundays?|(?:(?:mon|tues?|weds?|thu(?:rs|r)?|fri|sat|sun)s?.?))(?!(?:,|s+ands+|s+&s+))

on mondays,

on monday

on mondays?b(?!s*(and|[&,]))