Is zakat al-fitr waived with the passage of time?
Question

What is the ruling on one who does the obligatory duties of prayer and fasting, but he does not pay zakat al-fitr out of carelessness?
Praise be to Allah.Zakat al-Fitr is obligatory upon every Muslim who is obliged to spend on himself, if he has surplus to his and his dependents’ needs for the day and night of Eid; he must give one saa‘ of food, because of the report narrated by Ibn ‘Umar (may Allah be pleased with him) who said: The Messenger of Allah (blessings and peace of Allah be upon him) enjoined zakat al-fitr at the end of Ramadan upon the people, a saa‘ of dates or a saa‘ of barley, to be given on behalf of everyone, free or slave, male or female, among the Muslims.
Narrated by al-Bukhaari (1503) and Muslim (984) 
An-Nawawi (may Allah have mercy on him) said: al-Bayhaqi said: The scholars are unanimously agreed that sadaqat al-fitr (zakat al-fitr) is obligatory. Ibn al-Mundhir also narrated in al-Ashraaf that there was consensus on this matter. End quote. 
It says in Nayl al-Awtaar (4/218): With regard to delaying it until after the day of Eid, Ibn Ruslaan said: That is haraam according to consensus, because it is an obligatory zakaah. So it must be a sin to delay it, as is the case with delaying prayer until the time for it ends. End quote. 
The one who has not given it must give it for past years, and also repent and pray for forgiveness, because it is the right of the poor and needy, so it cannot be waived; rather it must be given to them. 
The four madhhabs (schools of thought) are agreed on this. 
Al-‘Abbaadi, who was one of the Hanafis, said: If they delay it until after the day of (Eid) al-Fitr, it is not waived and they must give it… even if it a long time has passed since it was due … End quote from al-Jawharah al-Nayyirah (1/135) 
In Mawaahib al-Jaleel Sharh Mukhtasar Khaleel (2/376) it says: It is not waived when the time for it is over. It says in al-Mudawwanah: If the one who can afford it delays it, he must make it up for past years. End quote. 
It says in Mughni al-Muhtaaj (2/122): It is haraam to delay it until after the day of Eid, unless there is a valid excuse, such as not having access to one’s wealth, or there not being any people who are entitled to it, because that leads to missing out on the purpose for which it was ordained, which is to make them independent of any need to ask of people on the day of the celebration. If a person delays it with no excuse, he is sinning and must make it up. End quote. 
Al-Mirdaawi said in al-Insaaf (3/177): The obligation of zakat al-fitr is not waived by death or anything else once it has become obligatory; there is no scholarly difference of opinion (concerning this) as far as I know. End quote. 
The scholars of the Standing Committee for Issuing Fatwas (al-Lajnah ad-Daa’imah li’l-Ifta, 9/386) were asked: What is the ruling on someone who was able to give zakat al-fitr but did not? 
They replied: 
The one who did not give zakat al-fitr must repent to Allah, may He be glorified and exalted, and ask Him for forgiveness, because he has sinned by withholding it. He must also give it to those who are entitled to it, although after the Eid prayer it is regarded as ordinary charity. End quote. 
And Allah knows best.