When might this buyback start?
I believe that they do not actually have to proceed with the buy back at all, and even if they do, they do not have to buy back that full amount.
Certainly there is no evidence of it having started yet.
What evidence do you want; maybe a personal call from Ma? Smalls has tried to explain the complexities of executions in terms of price paid and volume. It has started and continues imho.
Buy backs dont usually start with announcement of. They will most probably proceed when there is volume.