From NanoRacks, a few minutes ago—
The Module 9 mix sticks were activated by crew member Don Pettit at exactly 9:30 AM CDT (14:30 GMT) on Monday morning. He called down a couple of times wanting to make sure that he got sufficient bending (~5 degrees) to break the ampules, as he was having a hard time hearing the ampules over the ISS background noise. This much bending should be sufficient to get ampoule breakage.
The activation was delayed several hours due to Dragon cargo ops (another crew member needed his assistance to unpack the Dragon). He requested a call up from the ground at 3:30 PM CDT (20:30 GMT) to get the proper time for deactivation of the stick that has a six hour lifetime. The call up is necessary because it will occur just before his sleep period.