My ex has not been in our sons life since he was born. He probably spent not even 24 hours all together and he is 5 months. Can he get overnight visits when he hasn't established a bond or gotten to know him yet?

If the child is an infant, and especially if the mother is breastfeeding, overnight visits are unlikely to be granted. However, as soon as the child is weaned, if there is no other reason not to, the father should be able to get overnights.