I want to know is taking possession in this case is legal ? What is the time frame the authority takes to issue completion certificate to builder ?\
There is a news reported in the Times of India newspaper in this regard which is reproduced below:
GREATER NOIDA: The Greater Noida Industrial Development Authority (GNIDA) on Saturday issued a public notice, saying builders can't hand over possession of residential units to buyers without first acquiring the completion certificate, and warned of strict action if norms are not followed.
A senior GNIDA official said it is mandatory for developers under provisions of the Uttar Pradesh Apartment Act 2010 to get the original building plan sanctioned from the development authority, and sell apartments only after acquiring the completion certificate for the building.
"Completion certificate must be obtained and deed of apartment must be executed and registered by builder before giving possession of an apartment," said the official.
Officials said, the move follows repeated complaints from residents and home buyers that developers deviate from approved plans for their own gains and force them to take possession of flats without issuing completion certificates. Reportedly, when a group housing project is nearly complete, developers get the building plan amended with approvals for construction of additional apartments. By not obtaining completion certificates, they can bypass the sanctioned building plans and construct extra flats illegally.
GNIDA, through the public notice, also urged group housing allottees to report such builders who force them to take possession of residential units without the completion certificate.
"Such allottees can contact the GNIDA planning/architect cell, by writing to the general manager (planning and architecture). They can also inform the customer relations cell at GNIDA offices, or send an email to firstname.lastname@example.org. We will take action. The concerned developer will be dealt with very strictly," the official said.
In view of above, it is better you wait for the approval of completion certificate by the authorities to take possession.