Cron archive deletion / mass archive deletion

[Bob]

I am using freeBSD and just started tarsnap backups. I would like to 
understand a reasonable way to do periodic deletes via cron. I have 
named my backups "lilybackup-yyyy-mm-dd-hh:mm:ss". My hope is to be able 
to delete backups older than 30 days.

Thanks,
Bob