The time between the doors bursting open and the end of crossing blades with a guard is hardly immediate, though.  I hate to say it, but Senadra's gut instinct would be to fling at least one spell immediately on noticing a monster suddenly appearing, which would occur before Cimarron manages to say "Oops."  Both of her spells if she can manage it, though it'd probably be only one.  I can't speak for everyone, but the sudden appearance of a monster is enough to cause a combat action of some sort from most adventurers in my mind.