I have been thinking a little bit about extraction times ever since making a mildly unpleasent pot of coffee last week. The pot of coffee was mildly over-extracted, I had forgot to adjust the grind on my grinder going from a Hario v60 to my auto-dripper with a Melitta cone. The V60 with it's large hole requires a finer grind to slow down the water, however the adjustment in grinding really got me thinking about extraction times.
With most instuctions that you see online for pour over brewing people give a general time recommendations that will apply for all doses. Then you get people like me that want to follow those receipes to the T, and you get obessed over keeping that time at 3 minutes no matter how little or much you are making.
I just find it a little weird that people would be obsessed with keeping times right when just like you vary the amount of coffee you use to brew with the amount of water you are going to want to do the same with time. It just doesn't make sense to brew 8 ounces of water and 24 ounces of water for the same amount of time when doing a pour over..
Just really think about it for a moment, to brew 8 ounces of water in three minutes you will need to grind you coffee pretty fine for a pour over in order to slow down the flow of water enough to get that desired time. Since your grind is so fine you will be extracting a lot of solids out of the coffee, including the bitter flavors that are the last ones to get extracted, which will lead to a bad tasting cup of coffee. If you keep the grind the same through out your doses on a particular brewer, you should use a proportional amount of time when brewing just because you don't have as much water that needs to extract those solids from the coffee.
Basically what I am getting at is that say you brew on a Hario v60 and find a grind you like that gets the desired taste you want for 16 ounces of coffee in a 3 minutes pour, and next you want a 8 ounce cup, leave your grind the same and just accept that it's going to be a short brew.