Stuart Hallifax's search for the phrase in 1914 Britain turned up only one case, in November in the letters of an artillery officer (his article Home By Christmas can be found via google). It doesn't seem to have been widespread at all in the British forces, and the only similar saying in Germany was the Kaiser's promise that troops departing for the West would be home "before the leaves fall." While no doubt the soldiers on both sides would have hoped for some quick conclusion, by late 1914 it would have been clear that no swift end could be expected. I've answered a number of similar questions, which could be found in the user profiles section of the wiki.