Activating a scroll is a standard action, it doesn't matter the casting time of the original spell, because casting from a scroll is activating a spell completion item. Perhaps the devils knew the dragon would play with her prey and thus knew V would have the ~42 seconds needed for A. to get there and engage in battle, at least.
It doesn't matter if it would have worked or not - which I agree is debatable mostly so Kish and I don't get into another "could A. do it or not" discussion. Nothing indicates that V believed that option to be unworkable or bogus and therefore it was still a valid option in V's mind.