Guru Nanak Sahib ji graced the mortal coil in human form during pooranmashi (full moon). Since then, Sikhs have celebrated this anniversary every pooranmashi for hundreds of years.
Baba Nand Singh ji Kaleranwale has blessed the Sikh panth by teaching a viddhi (method) by which we may make spiritual progress by leaps and bounds. Those who remain awake on the night preceding the day of the pooranmashi will attain the spiritual merit of doing one month worth of amritvela. Those who remain awake the whole night preceding the pooranmashi of Guru Nanak Sahib Maharaj ji’s advent to this world will attain the kamai (merit) of one year worth of amritvela! The point is to remain in yaad of Guru Nanak sahib ji the whole night. This year pooranmashi of Guru Nanak Sahib ji’s prakash diharra is on the 21st of November. This means you need to start on the night of November 20 and continue at least until the sun rises (or as much as you possibly can do). Das has heard that Baba Nand Singh ji said that Guru ji took avtar at 12:21 AM.
People sometimes do nindya of such things as they fall outside the bounds of ordinary human logic. However Gurmat has its own logic, it is internally consistent. But this does not mean that one can figure out the ocean of Guru Granth Sahib ji through mere philosophizing. If that were true the ocean would in reality be a mere puddle. Gurbani unequivocally states that the bachan of a True Sant automatically comes true. Have sharda in your Guru’s bachan about the sants.