Hello @kannan.rpm, welcome to the community!
If I understood you correctly, then your flow looks something like this:
Postman (request) -> Your Server -> Some other server -> Your Server -> Postman (response)
And you want to know the time taken for
Your Server -> Some other server -> Your Server using Postman.
I am afraid that won’t be possible, because this other server is unknown to Postman/beyond reach and only the time between sending the request to your server and receiving the response from your server is known.
If I misunderstood you, please let me know and I’ll try my best to help you out.