question on notification on st tax

please tell me whether there is any notification regarding ceiling of service tax input credit upto the month of six month from the date of payment of bill or not?

Describing the case futher if i paid a bill of Rs112.36 including the service tax of Rs 12.36 at 1st april..is it necessary that i should utlise the input credit of Rs 12.36 with in the six month i.e. 31st september?

quick reply is expected....