They didn't use any technique, didn't activate their spirit bodies, and didn't show anything noticeable about their spirit elements.
She informed everyone and informed William first. The latter was already getting closer to her, only one hour away at most.
What delayed him was to arrange the huge influx of masters following him. He sent out many of his guild's top masters to help in leading others, getting advantage of this chance to deepen the impression everyone had of him.
A true leader shouldn't just win wars, but lead others to win their own battles as well. William tried to do that, and when he learnt about the incoming monster tide, he knew it was the right time to make a bold move.