How can i do performance testing of chat

I have 2 portals

• Staff portal (a web application)
• Member portal (a web application)

How to establish a chat

1. Send request from Member portal
2. Accept that request from Staff portal
3. Once the staff accept the request, they can start sending the messages

REQUIREMENT

1. I want to measure the response time of each message (How much time taken to reach message from Member portal to Staff portal?

CHALLENGES

1. How can i launch 2 applications (Member and Staff portal) and accept the request when 1000 members are sending request (I am using Silk performance tool/Jmeter, you can help me with any tool you know)
2. I can measure the time taken to send the message, but i couldn't measure the time when the message reach to staff.

Please let me know if you need any more information