Help with IBU contribution on flameout

[CaptainCookie]

Hey everybody, I'm a novice brewer working on an American Golden Ale and so far it's going well, but I feel it lacks aroma, so I'm willing to try a flameout addition of hops, but It concerns me the IBU contribution of this technique.

About the technique, I understand so far that consist about adding hops after turning off the heat, after the boiling is done, and cool the wort as quickly as possible for minimizing the bitter contribution of hops

I work with a 5 gallons kettle, and a copper immersion chiller, and it takes me about 20-30 minutes to cool the wort, with tap water, at pitching temperature, so my main concern Its how much this time will impact in my IBU count, I work with 25 IBUs

I've heard that is enough to just get to 174°F, at that temperature the Isomerization stops, and no more bitterness is produced, how true is this?

Also, how much hops do recommend for a 5 gallons baths for flameout? I'll use cascade

Thanks, Here a pic of my work so far

 

[ncbrewer]

Check out this BYO article: https://byo.com/mead/item/2808-hop-stands
This will answer most of your questions. One major point - it's common to do the hop stand before chilling to pitching temp. Sometimes that means chilling to somewhere below boiling, but hot enough to get the flavor/aroma - I do mine at 190F. At my temperature, I get the utilization equivalent of a 10 minute boil with a 30 minute hop stand - if that helps any. Good luck.