Even modern medicine agrees that sleep between 10 and 2 is the most important sleep of the night because many hormones, such as the human growth hormone, are released which ensure a balanced functioning of the physiology. The eyes are organs of Pitta and sight involves fire or light. Therefore, if you are awake after 10 pm, then Pitta becomes more active to keep you awake rather than to clean the channels of circulation and remove any ama (toxins) that has been accumulated.
Ayurveda also recommends waking up before 6 am, so that you awake under the influence of Vata, which is lightness and movement. If you awake under Vata, then you will bring those qualities with you throughout the day. Those who awake under the influence of Kapha (6am -10am) tend to feel more heavy and lazy throughout the day.