Since 1.0 it's been stated that the time it takes to teleport and arrive at the destination aetheryte is virtually instantaneous, the time it takes to travel through the Lifestream is barely perceptible (literally in the blink of an eye).

Of course we see a loading screen which can take ten to twenty, even thirty, seconds or more of real time to load, but as far as it goes in universe, it's instant.