5, 15 or 30 minute sequences. For longer simply repeat the chosen time. Japa is repetition of mantra. You can recite it in your mind as you listen, you can whisper it, you can speak it and you can even harmonize with it. Or you can mix it up. Do whatever keeps you as close and as present as possible with the mantra itself. Repeat as often as possible and let the magic unfold in your life.

Sanskrit
Asato Ma Sad Gamaya; Tamaso Ma Joytir Gamaya; Mrityor Ma Amritam Gamaya  Om Shanti Shanti Shanti 
Lead Us From Untruth To Truth, Lead Us From Darkness To Light, Lead Us From Death To Immortality, Let There Be Peace Peace Peace