nope this is speed on demand. not free double speed.
I just spoke to a airtel cce regarding this who transferred the call to technical department, she told me there was a double speed offer, but one would have to do a top up of 100 rs and get the speed doubled but with a limit, she told me it was 20 to 30 GB, after the limit exceeds, the speed would go back to the original. and this offer was not applicable to my plan anyway. my plan is 512 kpbs in day and 1 mbps in night. and this offer is not available anymore.