How much days are required to Transfer a Flat

I have a Flat in Andheri E. After the death of my father and elder brother, I and my mother are the only legal claimants or successors against the flat, my brother had a wife who claimed for the flat in court but we settled it outside court and paid her all the amount she asked and she provided all the documents releasing all her claims against the flat and removing her objections for us to stay, rent or sell the flat. All the Documents are provided by us to the Concerned Society, the secretary has issued us acceptance letter of Transfer of flat against our name. But after 8 months we are still waiting for the Transfer Letter or transfer of shares in our name. For seven months they did not allow us to give the flat on rent before this acceptance letter of transfer of flat, we suffered a huge loss 8 months ago. Now we require to sell this flat to buy another one and stay there. How much time do we have to wait. Is there a proper legal time period within which society should transfer a flat after collecting all the necessary documents and fees.