Where did date-time "add [custom] format" go in Drupal 7? In D6 this was located in,
Site Configuration &gt;&gt; date &amp; time &gt;&gt; formats &gt;&gt; add format
Where is this in D7?

I found this Drupal.SE question: Date value to different date format explaining the code to create a custom format, but it doesn't say in which file to make the change.
Configuration -> Regional &amp; Language -> Date and time -> Formats -> Add format.

You end up at /admin/config/regional/date-time/formats/add.