The xfce4-Timer-plugin is a handy addition to the xfce panel (avaiable in the repository for 7.1)
In addition to a count down it can set off an alarm with a command to run option.(note 24h clock)
If you install xmms for example you can put xmms /path/to/playlist.m3u in the command to run box and be alerted with a playlist of music.
The panel item has a toggle to start and stop timers when clicked or right click select properties to set alarms.
The panel item bar indicates time remaining and will show with a touch when alarm is active.
This makes an excellent alarm clock for your xfce desktop.