Since the ball was legally touched by A (after going 12 yards if I'm reading the free kick case play correctly), the clock should start since the ball has been legally touched in the field of play, and as soon as A has established both possession and control, the ball is dead by rule, and the clock should then stop. IMO a 2 second interval is probably correct here given the description of the down.
Rule 3 - Section 3: Starting and Stopping the Clock
ARTICLE 2. a. Free Kick. After the ball is free-kicked, the game clock shall be started on an official’s signal when the ball is legally touched in the field of play, or when it crosses the goal line after being touched legally by Team B in its end zone. It is subsequently stopped on an official’s signal when the ball is dead by rule.