19 September 2012
It based on the date of transaction for the purpose of service tax based on Point of taxation rules. In case the date of transaction is before 31-3-2012 then 10%+e.cess+she.cess in case it is after 31-3-2012 then 12%+e.cess+she.cess.
But remember for nov 2012 exams all the question regarding the dates on or before 31-3-2012.but due to the point of taxation the transaction date may comes later 31-3-2012.