I might be wrong, but I think it’s like this: A reading might take ~250 ms, i.e. the first reading after start-up. The extra time is supposedly needed for the sensor to initialize correct. In the latest lib for DHT22, only 1 ms (18 ms for DHT11) is used for the wake-up call and and the data transfer takes about 5 ms. That’s a total of 6 ms! Perhaps you just need to update your lib to make it go faster.