I have already answered a question similar to this here. Here follows a slightly modified answer.

The “Schlieffen Plan” is largely the product of Interbellum mythmaking by German officers who wished to deflect and minimise Germany’s failure to achieve a decisive victory in the summer of 1914. It helped these officers to create the impression that Count von Schlieffen had created a perfect, brilliant, unstoppable clockwork war plan that could have achieved victory over France, and would have done, had the safely-dead Moltke the Younger not modified the plan.

This was, to say the least, bunk. The German General Staff considered multiple war plans. Most historians today will argue that there was no singular "Schlieffen Plan". Rather, it is more appropriate to speak of a "Schlieffen concept", that envisioned defeating France first through an invasion of neutral Belgium, then turning to defeat Russia. Furthermore, there is a perception that the summer of 1914 was a "war by timetable": that once the mobilisation order was signed, an unstoppable clockwork war plan began that could not be stopped without a complete disaster. In fact, no nation was so tightly controlled, and the German Army in the tradition of Moltke the Elder would have recoiled at the idea of tying its Generals hands with almost no flexibility. The plans activated in 1914 were not "war plans", they were mobilisation plans, designed to concentrate forces on a particular are in the expectation of confronting a particular enemy, but they were appended with recommendations for marches and operations, with capacity for flexibility.

In 1914, the German Army had four mobilisation plans on file:

• Aufmarsch I West – Envisioned an isolated Franco-German war with possibility of Austrian and Italian aid. This is your “Classic Schlieffen” of the German Army making a massive sweep through Luxembourg and Belgium to encircle Paris and draw French Army into a pocket.
• Aufmarsch II West – Envisioned a German-Entente war with the possibility of British intervention on the side of the Entente. In this scenario 80% of German Army would be deployed in west and 20% in the east. An active defence would be conducted against both France and Russia, and French the French invasion force would be destroyed with a counteroffensive before Germany turned to defeat Russia. This was the mobilisation plan activated in 1914, but using the overall strategy envisioned in Aufmarsch I West.
• Aufmarsch I Ost – Similar to Aufmarsch II West, but deployed 60% of German Army against France and 40% against Russia, and launching counteroffensive against Russia first. This became a secondary plan since it was felt that a French attack might become too established to repel, and that France could not as easily absorb losses from a counteroffensive as Russia.
• Aufmarsch II Ost – Envisioned an isolated Russo-German war with an active defence in the east while holding the western frontier against possible French attack. This became a secondary plan after it was considered that an isolated Russo-German war was impossible.

In summary, the German General Staff had numerous military options available to them in 1914, any one of which might have helped to de-escalate or localise the war. There was no single “war plan” that had to be kicked off and let go to succeed according to a timetable. The mobilisation plans reflected political realities, even if the German leadership's view of those political realities was skewed. Indeed, in July 1914, Germany recognised the political value of allowing Russia to mobilise first. There even was the potential to alter mobilisation midway to rush troops to one front or the other should a political solution prevail with one of the Entente powers: owing to Moltke the Younger's own pessimism regarding France, he refused to enact that plan in 1914, to the disgust of the General Staff's railways chief, General Hermann von Staab, who wrote a book after the war to prove how it could be done!

In terms of sourcing, much of the modern understanding of "the Schlieffen Plan" (and how it wasn't) comes from Terence Zuber, which was summarised by Hew Strachan in his mammoth The First World War, Volume One: To Arms.