I usually give my samples between 20 minutes to an hour to breath, depending on the age. You'll notice that younger whiskies 10 to 12Y old need less time to breath usually, in my case, around 10 to 15 minutes. However it isn't sometimes true. I came across a very you whisky, 7Y old one, and after 20 minutes I felt that it was finally open it self up, because I gave it such a time to breath, very strange.
The interesting part is to snif every now and then in the time you let your dram breath to the air. See how it develloped minute after minute, until you say that's it and start to enjoy the pleasures of your dram.
Now people probably understand why I take 4 up to 5 hours for one dram of Bunnahabhain 1968, 34Y, because it develops all the time and that makes it such an enjoyment
But it's a good rule of thum what McEwen says about every minute for a year in the cask. It's slightly different then Patterson's conclusion to keep it in your mouth for a second a year it spend in the cask. Especially when it's a cask strength one
For what's it worth