Our planning Minister said it needs 2 decades, which I believe due to pressing needs for other allocation. Jokowi will have ceremony of our independence day in 2024 at that city according to the plan, but it is just a ceremonial event during our independence day, nothing more, even Jakarta I believe will still be a capital until 2029 or could be longer if Anies Baswedan become President.
If the President candidate like Anies Baswedan become Presiden, then it can take longer since he is not that enthusiastic about the idea to change the capital from Jakarta into Nusantara, but the development I believe will still continue despite him as our President starting in 2024 that could last until 2034.
President candidate like Ganjar Pranowo who is the most popular candidate by now is rather neutral on this, I never read he is supporting Jokowi idea on the capital change, he is not critical either like Anies, so he basically, IMO, like many Indonesian, who understand that it is a long term vision of ours to change the capital in order to make Indonesia more balance in economic development and less Java centric.
Despite so, Java will likely still be very important, including Jakarta. A new law to decide Jakarta position within our Republic after its role as Capital is taken out will come out soon. Almost all parliament members want Jakarta to keep its special status, not surprisingly since majority of parliament members are actually Jakartan (people of Jakarta). Mostly they are businessmen/women.