Dear
Each person is different , some person feel comfortable during late night period, some feel good in the morning
For late night study there is complete silence , and people can study peacefully if body permits , some people takes tea. coffee or chew gum while study to stay awake, these people are fortunate becouse study hours are longer during this time.
People like me who are early riser are some what at loss, though they remain fit health wise but morning hours are very less at most 4.30 to 6.30 , there after you can not have that kind of concenteration. and early rise has difficulty studying after 10 , their body just switch off.similiarly late study people can not study in morning.
so you can not say which one is better it is individual choice , which duration is suitable for him.