Short answer
Many families hold Namakaranam around the 11th or 12th day after birth, while others wait weeks or months; any of these is fine. Choose a day that suits the baby and mother, check it in Find Good Times, and hold the naming outside Rahu Kalam. The baby's birth nakshatra (birth star) often guides the first letter of the name.
How ChiChakra reads this
ChiChakra looks at the day's Panchangam for your town and marks Rahu Kalam. For the name itself, tradition links each of the 27 nakshatras (lunar mansions) with starting syllables, which our answer on baby nakshatras explains.
Planning the ceremony
Put the baby's and mother's health first. If the customary day comes too soon, wait; a later good day is perfectly normal.
Shortlist days when close family can gather, check them in Find Good Times, and keep the naming moment out of Rahu Kalam.
Legal birth registration has its own deadline. Meet it whatever date you choose for the ceremony.
Good to know
Your priest may follow your community's own rules, so share the baby's birth time and place with them.