Google-calendar – Google Calendar recurring date: Saturday before third Sunday

Although Google Calendar doesn't allow you to create or modify arbitrary recurrence rules like "Saturday after second Tuesday", the iCalendar specification which it uses and understands is quite robust in this regard. Simply create a *.ics file for the event with a custom recurrence rule or RRULE.

For your example, note that since the second Tuesday of a month falls, by definition, between the 8th and the 14th (inclusive), the Saturday which follows four days after it must fall between the 12th and the 18th (inclusive). So for a four-hour monthly maintenance window event from 3am to 7am, you'll want something like:

BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20130112T030000
DTEND;TZID=America/New_York:20130112T070000
RRULE:FREQ=MONTHLY;BYDAY=SA;BYMONTHDAY=12,13,14,15,16,17,18
DESCRIPTION:
LOCATION:
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Microsoft Security Patch Maintenance Window
TRANSP:TRANSPARENT
END:VEVENT
END:VCALENDAR

To import the *.ics file: In the left-hand list of "My Calendars", click "Settings", then "Import Calendar" link. You can specify which calendar you'd like to import the event to, but you won't be able to edit its recurrence rule from within Google Calendar, aside from deleting the event and reimporting it.

If this helps, you may wish to read more about the flexibility offered by custom recurrence rules in the iCalendar specification.

I have done this many times, though only on Android. When you make a new event on Android, you go to Repetition and then type of repetition and then choose monthly, where you can specify a number day.

Edit: I just checked the desktop version for you, which works as well. When you make a new repeating event, first set it on the start day, then check the Repeat box, choose a Monthly event, and the option to make it a specific day is a radio button.