I think that even a single year might be too much, obviously depending on the way things develop in different places.
Russia, for example: IIRC the number of strikes was very high in the spring of 1914; give it one more year and things might get worse, not better. I'm not sure which railway or industrial projects were underway, but I'm a bit skeptic that whatever was in the pipeline would make a real difference in terms of war readiness (and this also assume there is no other crisis between Ottomans and Russians like it happened in 1913 after the appointment of Liman von Sanders as commander of the Ottoman troops in the Costantinople area).
As far as the Ottomans are concerned, the 12 extra months would make a significant impact on the Berlin-Baghdad railway (although not enough for completion, IIRC Damascus would be directly connected by railway to Costantinople); the two dreadnoughts would certainly make a difference in the Black sea, but their presence might make the Russians more reluctant to enter the war.
The internal situation of the UK might get significantly worse, not just about the Irish Home Rule but also because industrial strikes were significantly on the rise. UK might be more reluctant to commit to a war in the summer of 1915, and this might dampen French "enthusiasm" too (in particular if the French and the British factor in the impact of the Haber process, which I doubt had a significant impact over their decisions in 1914). IIRC industrial strikes were an issue in France too, or, to put it in another way, the socialist parties in western Europe were getting stronger and another 12 months might possibly make a difference in their support for a war.
A-H is as big an enigma as Russia: the re-negotiation of the Ausgleich is one year closer (which might make the Hungarians even more obstinate), Franz-Joseph is one year older and his relation with Franz Ferdinand is not going to get better, there might be internal strife either along ethnic lines or because of increased industrial strikes, the Austro-Italian crisis over Albania might get worse.
German decisions did not follow a full rational path (none of the participants in the war can be singled out on the basis of the rationality of their decisions, and there were a lot of agendas at play), but if Russia and/or A-H are perceived to be in trouble I think that would make Germany less impulsive and more ready to negotiate.
Italy would have replenished its ammunition reserves depleted during the war in Lybia, and this might make them less in a hurry to declare neutrality (although I think the end result would still be neutrality).