How to setup a test that logs many people in, and then sends a request from each user as fast as possible?

OK, so I have a JMeter setup so I can log into my app many users -and it works great. However, I have a need to test when -after being logged in-all the users simultaneously request a page. For example, 300 users login over a time frame (can be 5 seconds, 5 minutes, etc), but after all are logged in, in a split second all request the same page.

Any good tips or pointers in the documentation are appreciated!