Re: Warp Drive in Star Trek Into Darkness - [SPOILERS]
In that circumstance they're trying out untested engines for the first time, and no doubt no oen wants them doing in near Earth. Note that they go straight to warp from Earth orbit at the end of the movie, which refutes the idea that it's dangerous.
I think that's speculation. We don't know how long it is from Kirk's final words to the warp-out.
And I don't see how trying out the engines requires you to get to Neptune or anything.
And that's my opinion.