In the earlier years of his leadership, the Rebbe would come to his office at around 11 o'clock in the morning, and leave in the wee hours of the next morning—on a regular day, he would leave at around one in the morning, and on days when there were private audiences, he would leave much later, at times at five or six in the morning.
When the Rebbe would leave, he would usually take home with him some letters and drafts of his talks. The talks were submitted to the Rebbe for review before being published. The Rebbe would add scholarly notes and make hundreds of edits on these drafts of talks. By the next morning, the Rebbe would bring everything back with him, with responses and edits for the secretariat to send out.
The truth is that I do not know exactly how many hours the Rebbe would sleep in his home. However, after the Rebbe's heart attack in 1977, the Rebbe's office became a mini hospital and he slept there for over a month.
The Rebbe's aides remained there that entire month too, 24 hours a day. At that time, we realized that the Rebbe did not sleep for any long period of time. I remember that if the Rebbe went to sleep at 10 p.m., at 11:30 he was back up at his desk studying or responding to individuals' letters or attending to other tasks. Later on, the Rebbe would sleep for another hour or so.
Before going to sleep, the Rebbe would always prepare what he would be doing when he woke up, whether it was a scholarly book that he would study or letters that he would respond to when he woke up.
I heard that the Rebbe's father-in-law, the sixth Chabad Rebbe, Rabbi Yosef Yitzchak Schneersohn, of saintly memory, said about the Rebbe, "At 4 a.m. he is never sleeping; either he did not go to sleep, or he already woke up."
