In the SS2 powered flight video below, the feather deployment (not unlock) command is given at very low speed.
It's interesting that the SS1 simulation has the unlock command very close to the feather command (which seems natural), while the as-flown SS2 sequence moved the feather unlock much earlier (at speed of Mach 1.4). This has been stated to be because they were concerned that an unlock failure would result in a dangerous situation later in the nominal, high-altitude (300,000ft) flight when the mission could not be aborted. So they removed a single-point failure (unlock failure) by moving it to earlier in the flight, but consequently added a new single-point failure of incorrect unlock actuation (at high speed).