The Zohar discusses the study at night and brings the example of King David who used to wake up every midnight to study and praise the Torah. It is known that King David slept the length of sixty breaths of a horse. Rabbi Yehuda asks: if this is true then his sleep would’ve ended early in the night and not at midnight.
Rabbi Yossi explained that at the beginning of the night King David sat with the elders of his house and studied Torah. Then he went to sleep closer to midnight so he could wake up at midnight and continue the study with songs and praises.
When the soul leaves the body at night, the body experience one sixtieth part of death. The first 60 breaths less one is still in full life and after that the spirit of death comes into the body. King David was keeping himself away from any aspect of death so he woke up before the impure spirit could affect him.
After midnight the energy is shifted and the light begins to appear in the world. Waking up at that time and studying Torah connects the person with the energy of life, renewal and growth. When we join at the point of revelation of Light our prayers have better elevation.
For most people it’s hard to have such routine. I could do it easily every night before I had children. I used to wake up after midnight for one hour or more of study before going back to sleep. Now the work on the Daily Zohar keeps me awake until after midnight (early evening is for the family). Friday night is my best and favorite night to study. Since I don’t work on Shabbat I go to sleep earlier then usual and wake up after midnight to study, sometime until first light when I take a short nap and wake up again for Shabbat services.
I recommend making efforts to wake up at night to study. It could be very hard at the beginning but energizing and rewarding on a spiritual and even physical health because we get a better ‘dose’ of energy of life.