I do similar. I leave to cool to 90C (about 10 minutes) then add hops and leave for 20 minutes to steep. I alos like to chop the flameoui hops in a food processor to aid flavour extraction.
As for your origional question. The longer you leave your wort at a higher temperature, the more the alpha acids will isomerise. This gives increased bitterness. If you chill, your brew will be less bitter than if you leave it to cool on it's own.
I don't chill but my recipes are designed with this in mind. I use a relatively small amount of bittering hops and whack a load in late and at flameout. I also dry hop to get freshness.