It takes 12 hours. And a bucket. Says SFGate.
Recipes galore, including how to replicate Blue Bottle:
Blue Bottle’s New Orleans-Style Iced Coffee
Makes 4 to 5 cups coffee concentrate, enough for about 8 to 10 cups iced coffee
While my friends and I always tend to debate about turkish coffee vs espresso, Blue Bottle’s most popular iced coffee features chicory for a nutty nuance. The sweetened concentrate will last two days in the refrigerator. To keep the concentrate longer, add simple syrup to each glass as you make it.
1 pound coffee, coarsely ground
1 1/2 ounces dried chicory root (see Note)
2 1/2 quarts water
3 ounces simple syrup (see note)
4 to 5 cups milk
Instructions: Combine coffee, chicory and water in a large stockpot. Stir with a spoon to make sure all grounds are wet. Cover and let steep at room temperature for 8 to 12 hours. Strain through a fine mesh sieve into a large glass jar or pitcher. Stir in simple syrup, cover and refrigerate.
To serve, fill a tall glass with ice. Add equal parts coffee concentrate and milk, or to taste.
Note: Dried chicory root can be found in the spice section of well-stocked supermarkets or specialty grocers. To make simple syrup, bring 1 cup water and 1 cup sugar to a boil and simmer until sugar dissolves. Let mixture cool before using. The leftover syrup can be refrigerated for up to 1 month.