MtoS: most women's milk comes in between days 1 and 4 after the birth, with events like difficult birth, sleepy baby, separation of mother and baby making it towards day 4. It's unusual for it to be day 5 or later, but anyone whose been around bf women and heard stories will hear about milk not coming in till day 6, 7 or even later - but that is really, really, rare. Sometimes, like I said to pebbles, the mother thinks her milk hasn't come in, but it has. If the baby is weeing normally and pooing yellow stools, then it has come in.
If it really hasn't come in, the mother should be expressing long before this to get what colostrum she can to give to the baby, which will encourage her milk to come, and get calories and fluid into the baby, on top of ad lib feeding.
The not all that uncommon gap between the baby starting to get really hungry and the milk coming in is not days, but a few hours...babies really do not need formula in that time, but can be comforted by sucking, cuddling, whatever. It can be a difficult time, though.
Jaundiced babies used to be given formula routinely - that's no longer the case. If it's decided the jaundiced baby needs more than he is currently getting at the breast then the first options should be for the mum to be encouraged to express or to put the baby to the breast more often, helping this with skin to skin contact