How many days was the fastest shipping of Berglunds snabbkp's order?
Berglunds snabbkp is the CompanyName; fastest shipping = Min(Subtract(ShippedDate, OrderDate))
SELECT datediff(T2.ShippedDate, T2.OrderDate) FROM Customers AS T1 INNER JOIN Orders AS T2 ON T1.CustomerID = T2.CustomerID WHERE T1.CompanyName = 'Berglunds snabbkp' ORDER BY datediff(T2.ShippedDate, T2.OrderDate) LIMIT 1