Things aren't quite a simple as that chart might imply – you will not always get maximum aroma extraction at exactly seven minutes thirty seconds, and maximum flavor extraction at exactly 21 minutes, with huge fall-offs just a minute or two in either direction, regardless of hop varietal, wort characteristics, strength of boil, etc.
But, in general, aroma contributions come from throwing hops in in the last fifteen minutes or so (or dry hopping, or doing a hop stand... search those terms), flavor from 10 to 30 minutes, and not much other than bitterness from anything longer than 30 minutes, with more bitterness the longer you boil.
What you probably want to do is add an ounce or two of "late" hops (various additions in the last 20 minutes or so) and/or an ounce or two (more) of dry hopping. Search for clone recipes of some of your favorite hoppy commercial beers to get ideas about what varieties of hops might add the flavors/aromas you like.