Legal action against builder not providing NOC and delaying possession

Hello Sir, I would need NOC for selling apartment while builder even denied NOC for transfer of my loan and also mentioned that he cannot provide during selling as well since he provided NOC once during my purchase and applying of Home loan. But bank demands NOC again if i sell apartment to someone who will need bank loan. Now builder is very adamant and not picking my phone and no one replies to me from his office. I tried to convince him as much as possible. I want to know if i start legal proceedings - how much time does it consume since i cannot have buyer wait until i fight legally. Can i start legal process in advance due to uncertainty and get confirmation from him in advance that he would mot create any problem when i need NOC for selling or i can only take legal action if he denies NOC. Once i apply for NOC during selling process - he would consume much of time to ensure buyer is out of the deal. Is there any solution to this or any workaround for NOC that i can provide bank.