Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 8 · Marriage
विवाहः
नैवोद्वाहो ज्येष्ठपुत्रीपुत्रयोश्च परस्परम् ।ज्येष्ठमासे तयोरेकज्येष्ठे श्रेष्ठश्च नान्यथा ॥ ४२२ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 422.
An eldest son and an eldest daughter should not marry each other in the month of Jyeshtha. If only one of the two is eldest, it is fine. Not otherwise.
Simple meaning: Two eldest children should not marry in Jyeshtha. If only one is eldest, Jyeshtha is fine.
उत्पातग्रहणादूर्द्धं सप्ताहमखिलग्रहे ।
Avoid seven days after a total eclipse and three after a partial one.
ग्रस्तास्ते त्रिदिनं पूर्वं पश्चाद्ग्रस्तोदयेऽथवा ।
Avoid days around an eclipse: three days, or seven if it falls at midnight.
मासान्ते पंच दिवसांस्त्यजेद्रिक्तां तथाष्टमीम् ।
Avoid the last five days of the month, certain bad moon days and some yoga times.