I used to see such things as datehour, dateminute, etc, etc. If I manually add those to the search, they show up in "Interesting Fields".
Same with my custom fields in splunk/etc/apps/search/local/props.conf. If I add them to the search, they'll show up under "Interesting Fields".
If I go to "Extract New Fields", and click on a line, they show up as already defined.
Interesting fields only show up if there more that 20% of the events with that field. Having said that, what mode is your search set to? Interesting fields will not show in Fast mode. Try changing it to Smart or Verbose