Sort of a new all grain brewer, was reading a thread on recipe for a DIPA using Nelson hop, the recipe called for adding hops at flameout for 20 minutes. I had wondered about this for some time. But thought it was important to chill the wort as soon as possible. Seemed like you would not get much aroma if you added and then chilled using a plate chiller. A suggestion was that i could whirlpool for 10-20 minutes, or steep them for 20. Is 20 minutes a common length of time to let aroma hops still after flameout?