Ok, so it's a fairly straightforward idea, that I know is still technical:

I want to use the K2 Calendar module on my site, but instead of powering it by the date the article was published, use the date (or dates) added using the "dates" function in Extra Fields.

This is where it becomes technical, so bear with me...

I'm using the K2 Items to allow calendar functionality itself... Where this becomes a fun challenge is that some of the K2 items published could have 3 or 4 dates associated with it, so I can't exactly use the Date Created (as it ends up in the calendar once), and it's obviously not sensible to have to duplicate the page 3 or 4 times, considering in the feed, it ends up having multiple posts associated with it (and in a feed, having the same thing show up back to back? Totally looks like you messed up somehow.)

I'm totally comfortable with custom templates and doing really extreme modding to K2 (like, we're talking stuff like making full color k2 images show up on the front end as black and white, full screen, responsive backgrounds... I like to push my software sometimes!), but I've never really had a complete understanding on how date functionality works in php to begin with.

I also am not 100% sure how I could get the calendar to do the following, which is essentially the workflow I'm trying to achieve:

1. load a K2 item in the calendar
2. get the calendar to grab the data from the extra fields
3. process extra fields info inside the calendar module
4. extract only the fields that show dates, and have that override the dates used in the calendar's default functionality
5. get it to loop so that every date that is added will appear in the calendar module

If you have any suggestions, or further questions, I'm open!

Thanks!

I would suggest that you look for an extension that uses this functionality.
Have you tried looking at the JED or here: getk2.org/extend ?