Jatakarma is performed before cutting the naval-chord ( i.e., before separating the child from mother) and such needs no muhurta. Only when this samskara is not performed at the time of Nabhi-bandhana, the need of choosing muhurta will arise and in that case it is generally performed with Namakarana.
The first act in the Jata karma samskara is Medha Janana ( producing intelligence) in which the father feeds the new born child honey and ghee with his Anamika finger.
In the second act the father pronounces the names of various long living objects, there by blessing the child with long life. Ultimately the naval chord is cut and the child is separated from the mother.