Allah the Exalted states:
“It has been made lawful for you, on the nights of fasting, to be intimate with your spouses. They are a garment for you, and you are a garment for them. Allah knows that you were betraying yourselves, so He turned toward you in mercy and pardoned you. So now you may approach them and seek what Allah has decreed for you. Eat and drink until the white thread of dawn becomes distinct to you from the black thread of night. Then complete the fast until nightfall. And do not approach them while you are in retreat (iʿtikāf) in the mosques. These are the limits set by Allah, so do not approach them. Thus does Allah make His signs clear to people, so that they may remain mindful.”
(al-Baqarah, 2:187)
As clearly stated in this verse, marital relations during the nights of Ramaḍān—except for those who are in a state of iʿtikāf—have been made lawful. In other words, the prohibition of marital relations that applies while one is fasting during the day comes to an end with ifṭār and remains lifted until the beginning of dawn (imsāk).