The timetable thesis doesn't hold up that well. The Russians had no plans for a partial mobilization, and the tsar still ordered a partial mobilization (although the military did succeed in pressuring him to return to general mobilization within a few days). Germany not invading Belgium wouldn't have changed the course of the war all that much--Britain likely would have found another excuse to involve itself in the war had Belgian neutrality not been violated.

If you subscribe to the belief that the grand strategy of war should be left to the politicians and not the military, then the timetable excuse is gross dereliction of duty on the part of the military: the military is failing to provide plans for perfectly reasonable options that the government could wish to enact (i.e., limited war instead of total war).