Praise be to Allah.
The time for paying zakaat al-fitr does not begin after the Eid prayer, rather it starts after sunset on the last day of Ramadaan, which is the first night of the month of Shawwaal, and it ends with the Eid prayer. The Prophet (peace and blessings of Allaah be upon him) commanded that it should be paid before the prayer. Ibn ‘Abbaas (may Allaah be pleased with him) narrated that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever pays it before the prayer, it is accepted zakaah (i.e., zakaat al-fitr), and whoever pays it after the prayer, it is ordinary charity.” Narrated by Abu Dawood, 2/262-263, no. 1609; Ibn Maajah, 1/585, no. 1827; al-Daaraqutni, 2/138; al-Haakim, 1/409.
It is permissible to pay it one or two days before that, because of the report narrated by Ibn ‘Umar (may Allaah be pleased with him) who said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) enjoined sadaqat al-fitr in Ramadaan.” According to another report, they used to pay it one or two days before the end of Ramadaan.
Whoever delays it after its time has sinned, and he has to repent for delaying and give it to the poor.
And Allaah is the Source of strength.