Youth academy level 1 will need 28 days to product 2 player . Each update shorter 2 days. You can check the next day youngster come in your team by clicking the building section and click to academy.
in this time of waiting if you update your young academy. the day count will reset from the beginning (28 for level 1, 26 for level 3 ....)
You have to wait for your player before update YA