I would keep the late additions some what low as guidelines state that hop aroma should be low to moderate. With that being said its home brewing so go for it if you would like. If your looking to get aroma only without increasing the IBUs then you will want to add them as late as possible. I would suggest adding at 5 to zero minutes before knockout. If your using an immersion chiller, I'd drop in your sanitized chiller in the wort and drop in the hops and stir. This will help to cool the liquid faster and the whirlpool method will increase the hop aroma that carriers through. You could also consider dry hopping for aroma.
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