Generally, during the evening Sandhyavandanam, arghyam is offered before sunset and upasthAnam is performed after nakshatra ArOhanam; on Pradosham days, when must the arghyam and upasthAnam be performed? Must we decrease the number of times the mantram is chanted during japam?

During evening Sandhyavandanam, arghyam is offered while the sun is still present and upasthAnam is performed after the rise of nakshatra-s; it seems the query is asking that when one chant 108 Gayatri mantra-s on all other days since one is allowed to chant only 10 on Pradosham, must we wait for nakshatra ArOhanam for upasthAnam; generally, elders after offering arghyam at the appropriate time, chant Gayatri mantra for 10 times and wait for upasthAnam time; if not possible, is not wrong if the offering of arghyam and performance of upasthAnam are done with a slight deviation in timing; even on Pradosham days, Sandhyavandanam must be performed on time.