Hi Jon, 
I've pulled in live streams in the past using mplayer with the -dumpstream option (mplayer https://yoururl/stream.mp3 -dumpstream) and started and stopped the operation with atd (I never fully gotten my head around cron).
I'll take a look at streamripper. I like the sound of the option to specify the duration of the rip as an argument of the utility. 

Cheers
Marshall
