Observing sandhya-vandanm is a brahmincal duty and thus pertains to the brahma gayatri and not necessarily the other diksa mantras and gayatris. However, the practice of mantra dhyana at the three sandhyams is an excellent practice. It requires that one stop and meditate three times daily, observing the sun’s movements and thinking of the sun as a symbolic representation of God. This mandates a change of lyifestyle for most.
The sun is so important to us. Without it we would be dead. It speaks so loudly to us every day, but we do not hear its message. Those with very deep expereince of life tell us, ayur harati vai pumsam udyann astam ca yan asau “With the rising and setting of the sun everyone’s life is being taken away, except, that is, for one who is engaged in glorigfying Krsna,” tasyarte yat ksano nita uttamasloka vartaya (SB 2.3.17).
At any rate, it is hard to change one’s lifestyle in a society that does not lend to it. Still we should try. There is no need to chant one’s diksa mantras on the thread, if it is inconvenient. But one should not chant in a way that is less than meditative if one expects to derive any benefit from chanting.
One can chant one’s first mantra session after rising and bathing, and do it a second time before leaving for work. Leaving for work, although in the forenoon, takes the sadhaka into the day so to speak, following Kana into the forest. That is the beginning of what could be construed as one of three major blocks of time in one’s daily routine, the first being early, early morning, followed by leaving the house for work, followed by one’s return home for the balance of the day.