Praise be to Allah.
Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said:
With regard to how he reviewed it with him, I do not know how that was done.
With regard to whether it is mustahabb for people to gather to read Qur’aan together or for each person to read it individually, that depends on the person himself. If gathering with his brothers to study Qur’aan together will make him more focused and help him to learn better, then gathering with others is preferable, i.e., if gathering with others will make him have proper presence of mind and be more focused on pondering the meanings of the Qur’aan, and allow the opportunity to discuss the meanings, then that is better. But if it is the opposite then reading it on his own is better.
With regard to Jibreel reviewing the Qur’aan with the Prophet (peace and blessings of Allaah be upon him), that was for the purpose of making sure that the Prophet (peace and blessings of Allaah be upon him) memorized it.
With regard to the third part of your question – which is whether it is better to do that at night rather than during the day – the answer is yes, but a person may need to do other things which means that he cannot study Qur’aan at night, in which case he should study it more during the day.
So each person should look at what is best for him, because of the general meaning of the words of the Prophet (peace and blessings of Allaah be upon him): “Strive to do that which will benefit you.” So whatever is more beneficial for you, so long as it is not forbidden according to sharee’ah, is best.