OTOH, Earth is still visible through the windshield, which isn't credited with magnifying properties...
Probably just a few lightseconds, then, not even a full minute at warp. The flight is depicted as taking as long as Picard's fight with the Queen, but that may be a movie illusion and the flight may have been over while Picard still had an annoying cling-on to his ankle...
Vulcan attention oughtn't be hard to get. Troi claims they were passing through the system, which means they had warp drive (nobody would "pass through" a system in a sublight ship, as one wouldn't dedicate years of one's life to a trip and then not do anything at the destination, and one wouldn't aim through a system if the true destination lay elsewhere) and thus probably also the means to observe another such drive at a distance. That is, even if Troi is being truthful about the Vulcans not being there to specifically monitor Earth.
Of course, Troi doesn't say the Vulcans weren't there to monitor Earth. She sidesteps the issue, saying the Vulcans are on a survey mission but have no interest in Earth - which might mean (as we see in "Carbon Creek") that they monitor Earth on such survey missions but have no interest in it in the imperalistic sense.
Timo Saloniemi