If they were early, and remembered to hold block after inputting the move, there would be no penalty because they would simply remain blocking like nothing happened.
If they hit it perfectly, the armored move would activate on the 1 frame gap where they are out of block stun before the next move hits. The armor would absorb d1 or 2 and connect.
If they are 1 frame late, the armor move would activate on the same frame that d1 or 2 connects causing meter drain.
If they are more than one frame late, they get hit. This is because you need to release block and press it again to have it register as an additional input to be applied to the special input. If you are late, whichever hit of 3d12 will connect while you are not holding block.