Just to note to avoid confusion: your ship’s displayed direction and it starting to change the moment you hit warp is not attached to your ship’s movement vector.
So the displayed direction is independent of the game mechanic regarding the vector. This is why it sometimes happens that ships, usually slow to turn ones like freighters warp sideways or partially sideways as their ship’s displayed direction did not reach the warp direction yet, but their actual velocity vector did thus they enter warp regardless of that the ship’s displayed direction did not yet reach the proper direction.