Hops bittering/Aroma??

When adding the hops it asks for bittering or aroma. What time addition would if be considered Aroma and not bittering
30 mins 10 mins 1 min? If I add hops at 10 mins and check bittering/Aroma it changes the IBUs and Im trying to stay in the style  guidlines Im using leaf hops

thanks Beersmith found my answer with a search
Late addition hops (boiled for 5-10 minutes) add very little bitterness, and are used primarily for aroma. Bittering hops are usually added for the full boil time (60-90 minutes).

Generally speaking 15 minutes are flavor 0-5 minutes are aroma and 15-whenever are bittering.  

The alpha acids isomerize during the boil at a generally predictable rate.  The flavor compounds (phenols) are not all that water soluable and tend to volatilize and vaporize and leave the wort for a better place much quicker that the humulones isomerize.  A rule of thumb is to use the above numbers.  

Additionally, consider removing your hop additions at flameout (unless using flameout / whirlpool hops).  Also consider that flameout/whirlpool hops will isomerize at close to the full rate depending on time and temperature.  An old idea that 5% utilization could be expected is not correct.  If you take 60 minutes to chill to xfter temp then you can expect upwards of 60-70% utilization.  

This means that if your beers are more bitter than you like, remove the hops at flameout and cut back on the flameout/whirlpool hops.

- Joe