As I have said before, Obama, Kerry and the USA are at a distinct disadvantage and are in a position of weakness by having a deadline to work against.
Anybody that has no need or fear of failing to meet the deadline is in a stronger negotiating position.

The French are trying to push back on the self imposed USA deadline:
How France Became an Iran Hawk | Foreign Policy

A major indicator of the amateur status of the US players on the world stage.