If the system processes a request for more than 3 seconds, is the loader displayed & is there a hint of how much time processing will take (in seconds or visually)?

Whenever users interact with a system, they need to know whether the interaction was successful. Appropriate feedback for a user action is perhaps the most basic guideline of user-interface design. So, such feedback can be as simple as a progress indicator when a process needs a little longer to finish. Check these examples: