Praise be to Allah.
The expiation for having intercourse during the day in Ramadan, like the expiation for zihaar, is to free a slave; if that is not possible, then he must fast for two consecutive months. If he is not able to do that, then he must feed sixty poor persons, because of the report narrated by al-Bukhaari (6709) and Muslim (1111) from Abu Hurayrah, who said: A man came to the Prophet (blessings and peace of Allah be upon him) and said: I am doomed! He said: “What is the matter with you?” He said: I had intercourse with my wife in Ramadan. He said: “Are you able to free a slave?” He said: No. He said: “Are you able to fast for two consecutive months?” He said: No. He said: “Are you able to feed sixty poor persons?” He said: No. He said: “Sit down.” So he sat down. Then a large basket of dates was brought to the Prophet (blessings and peace of Allah be upon him). He said: “Take this, and give it in charity.” He said: To someone poorer than us? The Prophet (blessings and peace of Allah be upon him) smiled so broadly that his eyeteeth could be seen, and he said: “Feed it to your dependents.”
But in the case of zihaar, it is haraam for the husband to have intercourse with his wife before having offered expiation, because Allah, may He be exalted, says (interpretation of the meaning):
“And those who pronounce zihaar from their wives and then [wish to] go back on what they said - then [there must be] the freeing of a slave before they touch one another. That is what you are admonished thereby; and Allah is Acquainted with what you do.
And he who does not find [a slave] - then a fast for two months consecutively before they touch one another; and he who is unable - then the feeding of sixty poor persons. That is for you to believe [completely] in Allah and His Messenger; and those are the limits [set by] Allah. And for the disbelievers is a painful punishment”
With regard to expiation for having intercourse during the day in Ramadan and expiation for accidental killing, it is permissible to have intercourse before beginning the expiation and it is permissible during the nights of the two consecutive months.
It says in Kashshaaf al-Qinaa‘ (2/327): In this case, it is not haraam to have intercourse before offering expiation, or during the nights of the expiatory fast. This was mentioned in ar-Ri‘aayah and at-Talkhees. That is like the expiation for accidental killing, and is in contrast to the expiation for zihaar. The difference between them is clear. End quote.
And Allah knows best.a