It aways lost the “Now Time Line” when I use the Surface Dial for Zoom in Zoom out。 and the “now time line” is not focus on the middle of the screen。

Are you placing the Dial on screen? (Surface 5 or Studio)?
In that case it will zoom around the position not the time.
If the Dial is not in contact with the screen, it's using the left edge of the view.
 
Sounds like it would be more useful (and consistent with Ctrl + Left/Right) to zoom around the now time if the Dial is not in contact with the screen.