Here is your short paragraph on Upakarma and Gayatri Japam:
This belongs exclusively to the Brahmins. In Tamil Nadu, they are called twice – born, dvija.
The first from the mother’s womb and the second from the Upanayana (thread bearing ceremony) which literally means an additional eye.
The guru who initiates are with the Gayatri Mahamantra becomes an eye opener and the youth develops this new sight by his learning.
On this day Vedas are recited, homa libation of water (darppana) are performed and the wearing new threads. Those who follow the Rig Veda observe the ceremony in the month of Avani on the Sravana asterism day.
If Yajurveda is followed, the ceremony falls in the month of Avani on the full moon day when Avittam is the asterisms. It there is some defects on that day, it should be observed in the month of Purattasi (September – October).
The ceremony occurs in the month of Avani with the asterism Hasta, if one follows the Sama Veda. The day succeeding the Upakarma, is the day of Gayathri Japam, when people sit in a pure and solitary place devoid of any disturbances and repeat the mantra ten, twenty-eight or one hundred and eight times without any breaks or internals, according to their convince. It is a part of (“Sandhya vandhanam” in the morning, midday and evening, besides the occasion of Upanayana.