When Should Zakat al-Fitr Be Paid?
Question

Is the time for paying zakat al-fitr from after the prayer until the end of that day?
Praise be to Allah.Time for paying zakat al-fitr
The time for paying zakat al-fitr does not begin after the ‘Eid prayer, rather it starts after sunset on the last day of Ramadan, which is the first night of the month of Shawwal, and it ends with the ‘Eid prayer. 
The Prophet (peace and blessings of Allah be upon him) commanded that zakat al-fitr should be paid before the prayer. Ibn 'Abbas (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) said: “Whoever pays it before the prayer, it is an accepted zakah (i.e., zakat al-fitr), and whoever pays it after the prayer, it is ordinary charity.” (Narrated by Abu Dawud, 2/262-263, no. 1609; Ibn Majah, 1/585, no. 1827; al-Daraqutni, 2/138; al-Hakim, 1/409)
Can you pay zakat al-fitr early?
It is permissible to pay it one or two days before that, because of the report narrated by Ibn ‘Umar (may Allah be pleased with him) who said: “The Messenger of Allah (peace and blessings of Allah be upon him) enjoined sadaqat al-fitr in Ramadan.” 
According to another report, they used to pay it one or two days before the end of Ramadan.  
Whoever delays it after its time has sinned, and he has to repent for delaying and give it to the poor. 
For more about zakat al-fitr, please see these answers: 235361 , 145563 , 124965 and 233593 .
And Allah is the Source of strength. 
And Allah knows best.