Namaskaram,
Swamy, while awaiting Sri Velukkudi Swamigal’s reply, Adiyen would like to share my experience/practise on such scenario (as guided by my aAcharyan).
Both of adiyean’s parents attained aAcharyan Thiruvadi on “Ekadasi” Tithi. Adiyen had the same doubt earlier which was later clarified by my aAcharyan. Some differed in their opinions/suggestion; however, later, adiyen consulted with aAcharyan and got clarified crystal clear. This emphasizes the importance of aAcharya sambandam/anugraham.
In the panchangam, on the particular day, if you see that “Srardha thithi” is Ekadasi and the Ekadasi Vratham is also on the same day then the srardham can be done on Dwadasi (following)day. This is to avoid feeding on Ekadasi day. If “Srardha thithi” is Ekadasi but no Ekadasi Vratham, then you can do Srardham on this day itself. (please check which Ekadasi you are normally following- smartha or vaishnava).
On Dwadasi day, you can extend the fasting till the completion of Srardham ritual – might be between 2 and 3.30pm?
Now, comes to the core issue. (Dharma Sangadam).. adiyen can recollect from Swamigal’s pravachanams and try compare/apply it here.
On one occasion, Sri koorathazhwan (Emberumaanaar’s closest Shishya) had to postpone his nithya anushtanam – evening sandhyavandanam to have perumal darshan in the evening. When one of his shishya reminded him of this, Sri Kooresar told him that Nithya anushtaanam could be performed later with Prayachithartham; however, Perumal darshanam would not get again if missed once on that particular occasion. Of Course, Bhagavan’s darshan takes precedence.
Srardham is performed yearly whereas Ekadasi is celebrated two weeks once per month. Both are done to fulfil Bhagwan’s preethi( or to comply with Shastras).Bhagavan accepts this, adiyen believe.
Shamiikanum for any misguidance/mistakes.
Awaiting Swamigal’s response.
Adiyen Ramanuja dasan.