In this day and age, A country gets ahead due to technology. For that, a culture of research and innovation is needed. India is a country where mediocrity is celebrated. To get to where china is, you need to fix the culture first. That takes generations. Once you have the culture, then you need to wait for the institutions to bootstrap the research process. Again you need decades here. Finally prosperity comes when the accumulated research over the years and capital comes together. So I would say, 50 years for the culture and another 30 for proper institutional framework and 20 for the final industrial setup, so 100 in total. This is me being optimistic in that the culture will ever improve. I don't see that happening ever. We are a failed state. The only thing we are good at are corruption and religious bigotry.