Please, do tell, of all the fresh college grads that get hired for dev/SWE jobs at Big N companies, how many have specialized skills that will bring value from

Please, do tell, of all the fresh college grads that get hired for dev/SWE jobs at Big N companies, how many have specialized skills that will bring value from day 1? In fact, how many weeks / months / years does it take for someone to become a consistent value-add contributor to ANY company?