Is there any time frame for adding service extra even after purchasing of general order?

Is there any time frame for adding service extra even after purchasing of general order?

Hi As per as I know we can purchase more service even after purchasing general order. And I heard from many buyer they do not see any option to buy more extra service with general order. And they cannot add more service as extra purchase. As per as I know there has no time and frame and buyer can add extra anytime. But still I confused really is there no any time frame for purchasing gig extra? I hope someone get me very specific answer with this issue. And If no time frame so, how does it work for quick delivery service?

Let me know please and what is your advise?

Thanks by Ajlancer