gistfile1.txt

on a specific date
at a specific time

every n months, weeks, days
every n hours, minutes

every nth month, week, day
every nth hour, minute

every nth month of year
every nth week of month, year
every nth day of year, week, month
every nth hour, minute of day

every first, second, third, fourth, last weekday of month
first, second, third, fourth/last quarter

but not on: public holiday, sunday, birthday (skip specific known dates)

examples: 

event occurs on every third wednesday of a month, at 7pm or:
event occurs every third wednesday, at 7pm but not if it's a holiday.
event occurs on monday, wednesday, friday
event occurs once in three weeks counting from today. whenever that is. 

ideally I would have connected, preceeding scheduled notifications. ;)