How did they get to Metaluna so quickly?
One moment they're leaving Earth's gravity and the next - after transformation - they're approaching the aliens home planet.
Perhaps they went through some type of conduit joining up different parts of the Galaxy. I doubt even the Enterprise to get there so quickly even at warp 9.9.
I'm not sure how far away Metaluna was though - perhaps it was somewhere near the Kuiper belt which would explain things.