Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 7 · Samskara Muhurtas
संस्कारमुहूर्ताः
देशकालोपघाताद्यैः कालातिक्रमणं यदा ।अनस्तगे भृगावीज्ये तत्कार्ये चोत्तरायणे ॥ ३२८ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 328.
Sometimes the time is missed because of trouble in the place or the time. Then do that rite when Venus and Jupiter have not set. Do it in the uttarayana (the Sun's northward course).
Simple meaning: If the time is missed, do the rite when Venus and Jupiter are visible and the Sun moves north.
चरस्थिरमृदुक्षिप्रनक्षत्रे शुभवासरे ।
Choose a moving, fixed, soft or quick star on a good weekday, when the child and father have Moon and star strength.
शुभलग्ने शुभांशे च निधने शुद्धिसंयुते ।
For boys the 6th or 8th month, for girls the 5th, with a good rising sign and a clean 8th house.
सप्तमे मासि वा कार्यं नवान्नप्राशनं शुभम् ।
The first grain feeding is done in the 7th month, on days other than empty, lost, Nanda, 8th and 12th moon days.