We have a semi-annual reporting process where an email is sent out to associates on a specified date twice a year. Is there a way that Nintex can trigger off of that calendar appointment to send the email?
a calendar appointment is just a regularSharePoint list element displayed in a certain view. So you can trigger a workflow when an appointment is created.
But if you know that specific date and it only occurs 2 times a year, you could also create a site workflow and schedule this workflow manually. I think that would be the easiest thing to do for you.
I think the key point of the original question was the one about these being recurring appointments, so it's not so much about when the item is created, but the data it stores about the future re-occurrence dates. If the calaculation of the dates isn't trivial (for example I imagine the meetings always have to be on a work day) then you're into hand-entering the reminder dates, e.g. by storing them in a "meeting reminder dates" list that someone has to maintain.
I don't know exactly how Sharepoint stores recurrence information, but I think Scott is probably correct in thinking this might be tricky to accomplish. A quick Google search says that calendars use a special custom column type for recurrence, and that column can't be added to any other type of list. It is supported by server-side code to do the recurrence date calculations.
My guess is that even if you can access the calandar list data, to do this in Nintex you'd end up having to re-implement the logic that Microsoft wrote to support that special column type, to turn a rule like "bi-weekly on wednesday at 1pm" into a date+time you can compare with (say) "Now + 7 days".
To be honest you best bet is probably to synchronise the calendar with Outlook on your machine (or the teams admin's machine), and use Outlook to send out the invitations. There may also be 3rd party addons for Sharepoint that can help accomplish this.
Otherwise, for 2 meetings a year having a manually maintained list of dates might be manageable, but there's always the risk if (say) a meeting date changes in the calendar, this doesn't get reflected in the reminder tool.