Acceptable to wish someone "happy Eid" before the end of Ramadan?

Is wishing a Muslim person "happy Eid" before the day of Eid al-Fitr something which is done in Islamic culture? In my case, I have a work-friend who I typically see once a week at work. I am *fairly certain* they are fasting for Ramadan. Would it be better to wish them "happy Eid" a few days **before**, or a few days **after** June 15th? Or is there no difference? As I understand it, Eid al-Fitr is a celebration of *the end* of a month of fasting, so I wasn't sure if it would be appropriate to congratulate them on the conclusion of the month while they are *still fasting*.