Generally, an S corporation must file Form 1120S by the 15th day of the third month after the end of its tax year. For calendar year corporations, the due date is March 15, 2010.
See IRS instructions - http://www.irs.gov/pub/irs-pdf/i1120s.pdf
Michigan MBT annual Returns are due the last day of the 4th month after tax year end with payment of final liability. Taxpayers (other than Insurance Companies or Financial Organizations) are not required to file or pay if apportioned gross receipts are less than $350,000. - http://www.michigan.gov/taxes/0,1607,7-238-47449-174211--F,00.html