Depends on how much time you want to or have. When I don’t have too much time I’ll do it for 5 to 10 mins. When I have time, 20 to 30 mins to clear my mind, emotions and feel the breath of my own. Listen to jazz or ambient sounds, so your mind won’t wander into a depressed state. Let your mind relax and take heed to what it’s telling you.
Although music is fine if on a timer, if you are similar to my personality, music is always a spiritual “wake up” call! So an alternative might be to make a calming tea and set it by your nightstand. You might have a reading source such as a book or magazine to read just to allow you to feel drowsy and then set it down on your nightstand.