see the manual at "working with a linear input"
"RadioBOSS lets you add a line input to a playlist. Line input settings can be configured via Options on the Input tab.
Line input is useful for retransmitting a signal received via the sound card’s input (e.g., a satellite feed).
To use the line input, select Playlist -> Add Line Input... in the top menu bar.
A window will open where you can set the duration (how long you want the Line.In to play). Optionally, you can enter a broadcast title."
Also see "Scheduling playback" and "Scheduled event"