If Jatakarma is not performed in time, it should be performed with Namakaranam. Both Jatakarma and Namakaranam should be performed on 11th or 12th day of the birth or according to the family tradtions. If this is done no specific muhurta is needed. If the above samskaras are not performed in time, following considerations are necessary for choosing a proper muhurta.
Nakshatras: All fixed nakshatras (Uttara Triam and Rohini), all movable nakshatras (Swati, Punarvasu, Sravanam, Dhanishta and Satabhisham), all friendly nakshatras ( Mrigasira, Revati, Chitra and Anuradha) and all short nakshatras ( Hasta, Pushyami and Abhijit) are considered good for both Jatakarma and Namakaranam.
Days: Monday, Wednesday, Thursday and Friday are good.
Tithis: 1,2,3,5,7,10,11,12,13 are good
Lagna: 2,5,8,11,3,6,7,9 signs are good. The lagna should be occupied or aspected by natural benefic planets.Proper