FMLA, when does employer tell you that you used days?

I have an FMLA question. You miss three weeks of work and return on the following Monday. Once you return, how long is it before management must tell you how many days they are charging you for against your 60 days FMLA.

One would assume that you missed 5 working days each week for a total of 15 days. Did they work any Saturdays? etc. I thought I read a case where an employer told an employee he had used 9 days and he challenged that decision because once he returned to work, the company had 2 or 3 days to tell him they were counting it against his FMLA leave or they couldn't count it against him at all.

I am trying to find that ruling.