It could take a few months depending on each child’s temperament. Most adjust after a month when they begin to understand the routine and what comes next in the day.
Does this child come full time or part time? Generally part time infants will take much longer to adjust than full timers.
I used to have a child like that. I had to put him down and carry on with the other needs of the other 4 kids. We basically had to carry on with the routine and tune him out. Give him some toys on the floor or in a cozy sitting area, and keep on with your normal routine
Praise him when he stops screaming.
That being said, some kids may not be suited for group care. Some need one on one like a nanny/grandma etc. Are there any developmental delays? That could complicate the transition process as well.
Give it another month, and then terminate. If he’s not already full time, suggest that, and see if it improves the behaviour. I only take infants/toddlers full time for exactly this reason. I don’t need a child screaming for 4 months because they can’t adjust to the variation in part time routine.
Good luck!