For example, even if you did not request an extension to file your 2010 tax return and actually filed your return on or before April 18, 2011 (because April 15 is a holiday in the District of Columbia), you have until October 17, 2011, to re-characterize your 2010 Roth IRA rollover or conversion.
FORBES: Before you get out the checkbook, second thoughts on your Roth IRA conversion...