This is from one of the Medicare fact sheets on Meaningful Use:
"For the first year for which an EP [eligible professional] applies for and receives an incentive payment, the EHR Reporting Period is 90 days for any continuous period beginning and ending within the year. For every year after the first payment year, the EHR reporting period is the entire year.
A Payment Year equals a Calendar Year (CY)."
So that seems to mean the deadline for adoption is 10/1/11 to get payment for 2011.