Perhaps lunchtime is the best time for your relaxation break. When you are learning a particular relaxation skill, it will probably take fifteen to thirty minutes to achieve a relaxed state. As your skill level increases, you may be able to relax more quickly. Different techniques may take more or less time. You are the best judge of how much time to spend.
Many people enjoy musical accompaniment for relaxation.
The point of any relaxation routine is to find your own internal music and rhythm, so make sure any external music enhances rather than interferes with that process. Falling asleep is fine if you're at home or at the beach, but dozing is not so fine if you're driving or at your desk. Set an alarm or timer if you're likely to fall asleep. Do not use relaxation techniques behind the wheel. Listen to your body.