Install it, upgrade magpierss if it advises you to do so, and a rich feed or set of feeds. Then you can set the update interval for each - Feeds->Update Scheduling, set the wait between polling to 24 hours.
To limit abuse feedwordpress will not let you poll every minute or something and in fact sometimes honours a feed's polling schedule over whatever you set in the Feeds preference. In those cases, you could set the new posts status to be Draft and go in once every 24 hours and publish those you wish to publish.