Interval means how often to check if the proximity sensor is covered. With 5000 you will just have to uncover the phone and wait between 0 and 5 seconds until timenow realizes there has been a change.

If you want to change the time the lock screen stays on after taking out of pocket you have to modify the timeout setting. The number is in milliseconds so setting in to 5000 means that light will stay on for about 5 seconds (up to 7).

This setting can't get lower than the default powerbutton press timeout, i.e. 1-2 seconds. (Nothing bad will happen, it just won't have any effect below a certain value)