sub rule (7) of Rule 4 of CENVAT Credit Rules, 2004 reads as follows:
(7) The CENVAT credit in respect of input service shall be allowed, on or after the day which payment is made of the value of input service and the service tax paid or payable as is indicated in invoice, bill or, as the case may be, challan referred to in rule 9. for payment of service tax sub-rule (1) of Rule 6 reads as follows:
“(1) The service tax shall be paid to the credit of the Central Government, -
(i) by the 6th day of the month, if the duty is deposited electronically through internet banking; and
(ii) by the 5th day of the month, in any other case,
immediately following the calendar month in which the payments are received, towards the value of taxable services :
Provided that where the assessee is an individual or proprietary firm or partnership firm, the service tax shall be paid to the credit of the Central Government by the 6th day of the month if the duty is deposited electronically through internet banking, or, in any other case, the 5th day of the month, as the case may be, immediately following the quarter in which the payments are received, towards the value of taxable services :
Provided further that notwithstanding the time of receipt of payment towards the value of services, no service tax shall be payable for the part or whole of the value of services, which is attributable to services provided during the period when such services were not taxable :
Provided also that the service tax on the value of taxable services received during the month of March, or the quarter ending in March, as the case may be, shall be paid to the credit of the Central Government by the 31st day of March of the calendar year.”.
Thefore it is clear you can take credit only when you make payment fot Service and service tax thereon. At the same time you have to make payment on the due dates after you realise the payment for services whether after providing service or in advance.