wort boils around 100*C, not sure how you're getting 120...
seriously tho, stopping the chill around 80-82*C and letting hops steep at that temp does great things for aroma. i've done this on IPAs, doing both a true flame-out addition and a 82*C/180*F hot-steep addition. smells amazing.
i believe, but am not certain, that 100-120*F is too low to be effective. at that point you're probably better off dry-hopping with those hops. you need some heat to effectively get the oils out of the hops in that short a time (that's why dry-hopping takes days, not minutes). what little you'd get with a few minutes at that temp will likely blow off during fermentation.
There's some misleading information out there. For example, Brad Smith states that the boiling point of Myrcene (which composes the largest proportion of hop oils) is 147F, when in fact it's 167C! (333F) http://beersmith.com/blog/2013/01/21/late-hop-additions-and-hop-oils-in-beer-brewing/ It is true that higher temperatures will increase the rate at which volatile compounds... volatilize, but higher temperatures also increase extraction efficiency. There is a lot of work to be done on hop oil extraction and temperature. As far as I know, there aren't any pro brewers out there who wait for the temperature to drop before adding post-boil hops, but it's a pretty new thing.