When to make request for c form!

We are pvt ltd company in mumbau. We have purchased software from ahmedabad based pvt ltd company of 5th Aug 2015. Now we have to give them C form. So when can i request for C form in MVAT website. I am filling VAT returns on half yearly basis. Should I make request in Oct 2015 or I can I make request for C Form today also? What is the connection between C form and VAT returns?