The Horde themselves say it many times.
Saurfang approved. The season of war would come again eventually, as it always did. No reason to rush.
“The boy in Stormwind will not start a war tomorrow,” Saurfang said.
On that, you and I agree. “Do you have your mind made up, Warchief? Are you driving us to war?* Despite the cost?”
“I see an opportunity. I need a plan to achieve it,” Sylvanas said.
“You are asking us to start a war with the Alliance,” he said.
“Does that trouble you?”
Lorash’s eyebrows twitched. “Not in the slightest. But you are not offering us enough of a reward. If you expect us to launch our attacks at the exact same time on the exact same day . . .” He sighed. “Some of us will have to strike at inopportune moments. That is a large risk.”