For my IPA's with no boil additions, I kill the heat, then add the hops as soon as all boiling activity stops. I put the lid on and give it a good stir every 5-10 minutes. I've steeped as long as 90 minutes, but I usually do 45 minutes to an hour.
For APA's and other hoppy brews where I want a controlled IBU level, I kill the heat and wait until my wort gets down to 185ish before adding my steep hops. I only brew 3 gallons, so I don't really have to use a chiller. 5 minutes of stirring with the lid off usually gets the temp down in the range I want.