(physically maybe it takes time but legally (halochekly)) it is **instant** 

why should heat be different than ([Shulchan Aruch - Yora Deaya 96.1][1]) cutting a (spicy) radish that after one cut (probably even if the knife is very sharp so very fast) we say that the taste traveled kdai nitila (the thickness of a finger)?


  [1]: http://beta.hebrewbooks.org/tursa.aspx?a=yd_x4264