Service tax payable on manpower contract bill

We are having Contract Workers through One Contractor.  For Apr'15 Wages, First we pay Wages + Service Charges + Service Tax 1/4 to Contractor on 6th.  Contractor will issue salary on 7 or 8th.  Contract Bill raised by him with May Month Date i.e., 6th May'15.  My Query is, whether we have to pay remaining 75% of Service Tax before 5th May  (or) 5th June.

Please Clarify.