Sandhyāvandana — the daily practice
After Upanayana, the young person is taught sandhyāvandana — the prayer at the junctions of the day, dawn and dusk (and in many traditions noon). It includes ācamana, prāṇāyāma, offering water to the Sun (arghya), and repeating the Gāyatrī mantra, often 108 times.
The thread is the outward sign; this daily practice is the real commitment. Even ten Gāyatrī repetitions a day keeps the promise alive.
Dawn, noon, dusk