midnight
`` The tunnel is finally completed , '' replied General Guph . `` How long will it take us to march to the Emerald City ? '' asked the Grand Gallipoot of the Growleywogs . `` If we start at midnight , '' replied the Nome King , `` we shall arrive at the Emerald City by daybreak . Then , while all the Oz people are sleeping , we will capture them and make them our slaves . After that we will destroy the city itself and march through the Land of Oz , burning and devastating as we go . '' `` Good ! ''