Okay, don't have my rule book here with me. But in Fed, if the punt was a "muff", and A recovers, doesn't the clock start on the "Ready" instead of the snap (since there was never a change of possession)? This is no different than when A gets a new series of down on a running play. The clock would start on the "ready" vs the "snap".

Now, if B caught the kick, and then fumbled, and A recovered the fumble, then the clock would start on the snap (change of possession).

Serg