What's the key to making the most of just 5 minutes?  Simplicity.  Music is made up of notes, but actually the silences between the notes is where a lot of the magic lives.  A 3 note melody, using the sustain pedal (the one on the right if you've got more than one on your piano) can provide all the ingredients you need - just press down the pedal, find the three notes with your fingers, close your eyes and play; let the notes and the silences be the only thing you concentrate on, and let the music take you away.  Try it - it's so easy to do, yet so effective as a de-stressing tool.