Towards the end of the songs menu there is an option for Playlist - choose, this, and length of 40 (minutes), and start playlist.
You can play about with the song list, and "skill" makes no difference, so you can either dance or sit down and listen to playlist.
Achievement will pop at the end of the final song - playlist may not be 40 minutes, for instance mine ran 33 minutes (notified on screen at end).
Let me know if you have any queries!