Yes, all player action is legal. I was making the point that there must be a "stop and 1-second PAUSE after a shift," but no pause is required before the snap begins when a single player moves to another position and then stops. But, he does have to come to a complete stop. Also, A40 is, indeed, stationary and within the tackle box at the snap, and his block below the waist on an opponent is within the tackle box AND from the front; thus, the block is legal.
The game clock is not addressed, but it would stop when A30 touched the ground out of bounds, and then would start when the referee signals after a replacement ball is spotted at the hash mark, and all officials are in position to officiate. While the ball is dead, the chains and down box should move to the succeeding spot, and be set as expediently as possible. The play clock would be set to 40 seconds and started immediately when the ball was signaled dead after the previous down.
Not all questions have to involve fouls, but they need to test our knowledge of rules.