To link an RSS feed to Postcron go to the Content Gallery on the side menu and select the RSS Reader.
Then, click on Add RSS Feed, paste its URL onto the pop-up, name the channel, and confirm by clicking +Add.
The newly added channel will show up under Your feeds and to load its content you just have to click on the search button (magnifying glass icon) right next to it.
Now, to schedule the links, you can use either your Predefined Times by clicking Add, or send them to the Composer by clicking Create to use other scheduling options and/or edit your post before scheduling.