When an opponent casts a spell, if Veiled Apparition is an enchantment, Veiled Apparition becomes a 3/3 Illusion creature with flying and "At the beginning of your upkeep, sacrifice Veiled Apparition unless you pay
."
A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.