The only way that chronology makes any sense at all is if we also take Spock at his word that the supernova was itself a threat to the entire galaxy and that he wasn't just talking about the political fallout of the destruction of Romulus. Why else would he "have little time" after the planet was destroyed and why would he even deploy the red matter if it didn't constitute an ongoing threat? Sadly, Romulus died because the movie needed a macguffin, something to tick off Nero and create a black hole.
I look forward to see if the effects of the loss of Vulcan are brought up in the next movie(s), particularly their effect on Spock. It's too bad that Bad Robot felt they had to take a parting shot at the prime universe on the way out the door.