In my view, ideally, after receiving the CP. As then only you will have the CP number which has to be written in most of the audit report/certification jobs.

Regards,

After receiving COP .

Yes, you can if you are confirmed about this by looking at COP on hand.

Until you receive the Certificate of Practice you can not sign the Balance Sheet. 

DEAR,

ONCE YOU RECEIV A LETTER FROM ICAI REGARDING COMFIRMATION OF YOUR CERTIFICATE OF PRACTICE, YOU CAN SIGN AND DO ATTEST FUNCTION AS LIKE OLD CHARTERED ACCOUNTANTS,,,,

GENERALLY, CERTIFICATE OF PRACTICE WILL BE EFFECTIVE FROM THE DATE ON WHICH YOU PAID THE FEES FOR THE SAME......

DONT WAIT FOR A LAMINATED CERTIFICATE OF PRACTICE FROM ICAI DEAR........ BECAUSE I HAVE RECEIVED MY CERTIFICATE OF PRACTICE AFTER ONE AND HALF YEAR LATE.......

I agreee with Ashish

COP is generally granted from the date when you had applied for the same

YES IT IS FROM THE DATE OF APPLYING FOR COP. I HAVE CONFIRMED THIS WITH CA INSTITUTE.