Is praying in the last third of the night four minutes before Fajr considered a lack of divine success? And is it permissible to write letters to God and conceal them from people?

"Qiyam al-Layl (night vigil prayer) is an act of great reward, and Allah has praised those who perform it. If someone is overcome by sleep or illness, preventing them from performing Qiyam al-Layl despite their intention to do so, they will attain the reward for what they intended, and their sleep will be considered charity for them, as established in the Hadith. It is recommended to make up for missed Qiyam al-Layl during the forenoon (Duha) time. So, whoever sleeps through their portion of the night and recites it between Fajr and Dhuhr prayers, it will be recorded for them as if they had recited it during the night. As for writing a message that includes supplication to Allah and asking for needs, there is no harm in it, but there is no need for it, for Allah is near, All-Hearing, and answers the supplication of the supplicant."