This habit is counterproductive for two reasons. Firstly, according to modern psychology – the brain works the best early in the mornings after one has rested for 6-7 hours. This is same fact has been stressed in the Vedas. The early morning hours – brahma muhurta are especially suited for intense spiritual practices of focusing the mind on God. It is a particularly good habit to wake up early and meditate on the names of God.. There is no better rejuvenator for the mind than this. Afterwards one can immediately start off with one’s studies. Most students tend to go late nights which is a dangerous for one’s health and detrimental for one’s studies. A simple way to understand this is through an analogy. If you would like to drive long distances what is the best time of the day to begin your journey? Early mornings!! Why? Because then the traffic on the roads is minimal and you have the whole day to complete a long journey. If one were to start in the evening one would be harassed by highway traffic and also would have to break his journey to rest for a while. Similarly, our mind keeps storing various impressions it receives during the day and when one sits for  studies in the evening or night these stored impressions act like highway traffic inhibiting our peak concentration levels. But a rest of 6-7 hours at night refreshes the mind so that early in the mornings we are at peak concentration levels. Secondly, sleeping late and waking late forms a habit that may play havoc with one’s performance on the final day of the exam. A habit of studying at night and resting in the day habituates the mind to be more focused at night and relaxed in the day but unfortunately competitive exams are held in the day and not at night, so one is losing one’s capacity for concentration during the day by studying at night.