Samskaras-Overview-2

Jatakarma was performed before the severing of the navel chord. This can change because of other factors like death in the family etc.
Namkarna is performed on tenth or twelth day after birth. There is again a wide option for the dates.
Each Rashi contain two and a half Nakhshatras. That is why when you go to a South Indian Temple, the priest wants to know your name, Gotra, and Nakshatra. This is more precise than Name, Gotra, and Rashi. Most of us know our Rashis but have no clue about the Nakhshatra. Ask your priest. This side discussion apart, the naming has a lot to do with the nakhshatra (Nakhetur in koshur).
Finally, I must again point out that ALL samaskaras among ALL Hindus are performed according to GrehaSutras. The details of Homas (havan), naming convention for Namkarna etc, are standard. The details vary according to the local traditions. For example, Kashmiris use Tantric symbols that are absent in all of South India. Kashmiris chant vedas in Sama (singing) style, whereas South Indians chant in very crisp measured style. The stuff they chant is exactly the same. The Dhrivyas (items for worship) are also local stuff. Naturally we use things we are used to, like walnuts and almonds, and Nabad (nabaat of persians). South Indians use coconut, palm leaves, etc. So, if you want to do any of these ceremonies here, go find a knowlegeable South Indian priest, tell him a few things about your own customs, and enjoy a genuine function. DO NOT ask them to use tantric signs they are taught to stay away from such stuff.
Background, texts, and rituals of the five major sets of Hindu samskaras: prenatal, natal, education, marriage and funeral. Also background on Hindu traditions.