For me, it would depend. Did the parents get the child ready for daycare? Do they coddle the child at home, or are they working with me to help the child settle? Does the child eat/sleep? It is constant crying or are there times when the child actually engages in the daycare?
If the child was non-stop crying the whole day and didn't seem comfortable at all. I would probably give them two weeks to adjust. However, if it wasn't constant, and the child was otherwise happy, I would probably give them a month, but have the parents know that the child was on notice.