It must be. After all, Spock got from Vulcan to Earth in the time between the Klingon encounter with Vejur and (a couple hours after) the Enterprise's launching, and that certainly wasn't four days.
But we don't know that Spock went all the way to Earth, as he's shown meeting the Enterprise
in a shuttle, which could have launched from Vulcan. And there's no indication of how much time passed between the Klingons encountering V'Ger and Kirk's arriving at Starfleet HQ, shortly after which he tells Scotty that V'Ger is less than three days from Earth.