You can create a scheduled recording with iCal by selecting the menu option "Scheduler --> Create iCal Event".
The following window will appear: If you invoke this menu option when you have an iRecordMusic browser window open, which is playing audio, the web address of the existing web page will be used.
Scheduled recordings are mute so that if they start in the background, while you doing something else, such as listening to iTunes or watching a QuickTime movie, you will not be disturbed. By default this is enabled.
Archived content is a non-live stream. For example, broadcasters often archive their old shows. When you listen to these streams, the audio player typically shows the length of the show e.g. 30 mins. In contrast, a live stream has no length as it is continuous.
You should enable this option if you are recording an archived show. The reason is because, as detailed above, iCal and iRecordMusic launch 2 minutes before the scheduled recording show to prepare the recording. Normally, web pages start playing immediately once they are loaded, so if you are recording an archived show, part of the show may start playing before the scheduled recording time. Enabling this option ensures that iRecordMusic starts recording as soon as the web page starts playing audio, instead of waiting the 2 minutes until the actual recording time.