I've website - that is about two years old and fast indexed in google - almost within 2/4 minutes. But for some change in requirements, I need to create either subdomain or directory in it's URL - my question if I do so, is it going to hamper it's indexing timing? Thanks in advance.
No, it would not get affected... especially if your new subdomain possess a targeted niche, the organic traffic might even increase.
No there will not any harmful to your site. If you create new directory than google will get some changes and new content in your site. And for subdomain it Google crawler can not differentiate domain and subdomain, it will treat it as normal URL.