For World War I to spread beyond an Austro-Serbian war, the other great powers have to either Declare war or cross a border. In OTL the war spread when the Germans declared war on Russia and sent their ultimatum to Belgium. The German declaration is made August 1 to cover the German planned invasion of Belgium/Luxembourg on August2. The British follow after the Belgium invasion on August 4.
If the Germans go East, however, there is no need to Declare War until the Germans either cross the Russian border or the Russians invade Germany or Austria. This then leaves France and Britain who must declare war or stay out.
So what do you think the timetable would be? Would Germany still declare war on August 2 or would they wait. IF they wait, how long can they and when do Britain and France join