The Feed Frequency setting can be found by clicking the Offline Data tab in your Control Panel.
Feed frequency controls how often orders are checked and sent as notifications.
What Feed Frequency should I set it to?
There is no right or wrong answer. Experiment and see what works best for you. As a rule of thumb, you want your average visitor to see 4 or 5 notifications during their visit, so check your analytics software to see on average how long customers spend on your site.
For example, if customers stay on your site for 5 mins (on average) then set the Feed Frequency to 60 seconds.
Now your customers will see 5 notifications as they browse your site.
If the average visit is 3 minutes, then set the feed frequency to 36 seconds.