Allah, the Blessed and Exalted, says: "Before they touch one another." [Surah al-Mujadilah: 3]
Imam al-Shafi'i (may Allah have mercy on him) said: "So if intercourse takes place before the expiation and the time (for the expiation) passes, the expiation is not nullified, and we do not add anything to it for him; just as it is said to someone: Perform the prayer at such-and-such a time and before such-and-such a time, then the time passes and he performs it (later), because it is obligatory upon him, and it is not said to him: Add to it because the time has passed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الظهار / Q15257