There is a brief moment of animation before and after the actual dash itself. This would account for you feeling there's a pause. First you rev up to dash, and then you settle down from dashing. As a side note, these moments of animation also cause dash to be about walking speed on the whole. You jump gaps faster, but someone walking would get there in the same amount of time. Well, the dasher would be a character length ahead, but that's not noteworthy.