Service TAx Paid on Import of Service

When one can avail the setoff for the Service tax paid on import of Service? At the time of payment of service tax to the dept or at the time of payment made to the party for availing Service.

Lets take an Eg:-

On 1-4-2010 Service Received by XYZ Ltd for Rs 100000/- from ABC .inc

On 1-6-2010 payment made to ABC Ltd.

On 1-9-2010 the amount of Service Tax i.e Rs 10300/- deposited through GAR7 to Dept.

In which month Service TAx setoff can be availed by XYZ Ltd

Thanx in Advance