Maybe they had some sort of throttle accident and got there via time dilation (from the crews perspective natch).
...But not from Kirk's, alas.
Yeah. Time dilation is a nice idea, but the edge of the galaxy is just too far for the Valiant
to get there at sublight speeds, before Kirk's Enterprise
gets to the edge itself. Even if the Valiant
went to a much different part of the barrier, and the disaster beacon drifted a long way, the edge of the galaxy is just too far from Earth, even at its shortest distance (presumably at least about 400 light years [http://en.wikipedia.org/wiki/Milky_W...d_neighborhood