After adding an API, you can set it to refresh periodically in the background once every 1/5/10/30 mins or 1/2/5/10/24 hours.
Although it is optional, it can be helpful when you don't want to refresh the data on-demand manually. Once you enable it, whenever you open Radar, the data is always up to date based on your auto-refresh frequency.
Click the Pencil icon of an API on the listing page, select Next. Now, in the dropdown, you can choose the frequency of auto-refresh.