Early victories are likely to be much less harsh than Brest Litovsk and Versailles were IOTL and even if Germany gets beaten in the West is still likely to make big gains in the east meaning a deal for status quo ante bellum is probably the outcome. Any gains Russia makes are likely to be at the expense of Austria Hungary since that's where her successes on the battlefield were.
Why would you thnk that? The speed iof the victory has little impact on the terms. It is the magnitude of the victory.
The Iran Iraqq War lasted neary a decade and ends with status quo ante bellum basically. The same in Korea
Some rather quick wars- the Franco-Prussian for example, result in pretty harsh terms The colonial warstended to be very short and the terms were usually annexation.
If the allies crush Germany the terms are likely to be very harsh even if the war is over in September 1914.
The competing interests of the allies will be the determining factor. Russia is more interested in destroying Austrian power than German. As no one would object, Austria is being dismembered with Russia, Italy, Romania and Serbia taking what they please
As for Germany, there are two options. Its power is either destroyed as in a Versailles like settlement or the y get off rather easily because it is in someone's interest to keep it strong. The French are likely to want to see it crushed, the Russians much less so. A strong Germany could prevent an Anglo-French anti-Russian alliance.
British interests are likely to be ignored in a short war scenario. The Germans aren't likely to care much about their colonies when the French and Russian armies are pouring into Germany The British lack an army to have any influence until 1916