In Yoga Philosophy, they correlate the sunrise with expansion (principle of prana) and the sunset with involution or contraction (principle of āpana). This principle is also connected to the equinox and the solstice. All of these times are seen as auspicious moments to engage in spiritual practice. There are quite a few differences, however, between the two times of day when it comes to a Yoga practice.
From the Yogic perspective the sunrise is when energy is increasing. This is why many people find it easier to be productive earlier in the morning. The sunset is when energy starts to wind down. Practicing as the sun sets naturally connects you to the softer side of Ashtanga. It is easier to connect to the meditative qualities because it is a natural time for inward reflection. This is perfect if you tend to have stress in your day, and sets you up to make healthy choices in the evening when we are most tempted to do the opposite.
One of the most important parts of health and happiness is sleep. Most importantly sleep that leaves us feeling restored, but the evenings are one of the hardest times to make healthy choices. Many evening activities we do to unwind stimulate our bodies and minds leading to restless sleep and over all low energy. The TV emits a blue light that has been shown to trick your nervous system into thinking it is day time. See Harvard health letter for more information on blue light http://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side. Many of our favorite comfort foods tend to be high in salt and sugar which create a stimulating effect on the brain. Having activities, such as evening Yoga, that allow you to destress and unwind before your evening have the opposite effect. It calms the nervous system, focusing the mind and releasing tension from the body to cultivate healthy routines in the evening.
When beginning a Yoga practice it is important to find a routine that works with your lifestyle. The real benefits of Yoga come with consistency, so it is best to make your evening practice a weekly habit. Whether it is one or six days a week, finding what works for you and sticking with it is what makes all the difference. At the Ashtanga Yoga Room we offer evening Mysore Style classes, Monday through Thursday, that are peaceful and sure to help you connect back to your center.