When a value is set for the keep alive interval setting, the browser will keep the server job from timing out by sending a keep-alive request every so often. The interval is specified in seconds. It is reset every time a new screen is rendered. The keep alive interval will NOT be in effect if the Client Side Timeout flag is true. To use the keep alive interval setting, you must set client side timeout monitoring to false.
This value should be set to an interval slightly shorter than the server session timeout. For example, if the session timeout is 1 hour, then sending a request every 55 minutes will keep the session active. Using a shorter interval would result in unnecessary requests.
Where do you save this configuration option? Here.