It "responded" immediately to the "command" (an onboard automatic trigger) and the explosive charges ruptured the tanks instantly. However, the explosive charges which ruptured the tanks didn't cause the vehicle to disintegrate immediately, as it was stronger than anticipated and at a high altitude with lower wind force. (No one has flown a rocket of this construction and size before.) The flight was, however, pretty well terminated at that point (the FT in FTS).

They will be adding more explosives for the future to ensure structural failure.