Assalamou aleikoum wa rahmatoullah wa barakatou
We are day 25 of Ramadan, Mashallah. Our Zakat ul Fitr will be able to be paid from the 28th onwards until before the Eid Prayer. But not after. And if Zakaat ul Fitr is paid after the Eid prayer, then the one paying it will only have made a normal sadaqah, and would have not discharged himself/herself from the duty of Zakaat Ul Fitr and therefore, would not benefit from it.
For those not yet acquainted with Zakaat ul Fitr, please read about it here
and you can read selected fatawa (islamic rulings) pertaining to Zakat ul Fitr here