Kabbalah zu Ejchah 2:19

However, if one studies during the day and he is satiated, he does not have to lengthen his study at night in a way that he cannot wake up at midnight. And “the wise man, his eyes are in his head” (Ecclesiastes 2:14) and will “order his affairs rightfully” (Psalms 112:5) in a way that he will deal with Torah during the day until he is satiated, and in the beginning of the night he will deal with Torah as well so that his soul can elevate by the breath of the Torah, but not to the point that he is satiated so he will not miss waking up at dawn, which is the main time to deal with Torah, as it says “Arise, cry out in the night, at the beginning of the watches [last part of the night]” (Lamentations 2:19).