This assertion tests that each response was received within a given amount of time. Any response that takes longer than the given number of time (milliseconds) specified by the user is marked as a failed response.
Let us look into an example :
Step 1. Right Click Test Plan > Add > Threads(Users) > Thread Group
Step 2. Thread Group > Add > Config Element > HTTP Request Default
Set Server Name as: google.com
Step 3. Thread Group>Add > Sampler > HTTP Request (Change name to Google Home Page)
Set Path as: /