When does baby bonding begin?

So I know we are all different, but when do new moms start feeling that bond with their babies?

I ask because I don't feel that bond yet at all, and I feel awful about it. This is my first child, and even though I love my son, I feel that immensely, I don't feel the desire to spend immense amount of time with him or sometimes even hold him. What is wrong with me? My son's basic needs are met, but I can't meet his familial and social needs. Will that change later? Will a bond with my son eventually develop? How do some moms feel that bond right away while others dont?

Oh, btw, my son is 4 months old. He arrived 10 weeks early scaring my hubby and I, but he is thriving now. He eats well, is clothed well, he is loved, but I don't feel the desire to personally interact with my son. Why? I feel like a bad monmy.