Service tax cenvat credit under rcm

Dear All,

We are service receiver under reverse charge mechanism ( service under manpower recruitment) , we paid 25% service tax to our service provide. From july-12

But we have not taken CENVAT credit of 25%  from july-12

1. My query is can we take CANVAT credit of 25% from july-12 to till date, what is the specific time/ period for take CENVAT credit?

Regards,

NITIN