to calibrate the sensor properly you should use a gas chamber and measure the output under different concentrations in the range of use. Your calibrated sensor will help you to determine the exact concentration in the chamber if you don't have a way to regulate it. After calibration, adjust the load resistor to match the sensor resistance at the middle of the desired measurement range.
Regarding the hibernate, you have an example here:http://www.libelium.com/development/waspmote/example035
The difference between hibernate and the other sleep modes is that the only device active in hibernate mode is the RTC, that triggers an interruption to wake up the mote after a given time or at a determined hour.
You can find more information in section 3.3 of the Waspmote Power Programming Guide.http://www.libelium.com/documentation/w ... _guide.pdf