All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
According to the preponderant of the scholars' relevant opinions, the time of slaughtering starts immediately after the 'Eed prayer and extends until the sunset of the last day of the Days of Tashreeq (the 11th, 12th and 13th of Thul-Hijjah). It was narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: "The Days of Tashreeq are all for sacrifice." [Ahmad and Ad-Daraqutni]
This means that the time when slaughtering is permissible extends over four days: the day of eid and the next three days, which are the days of Tashreeq. Whoever slaughters before the prayer or after the sunset of the 13th day of Thul-Hijjah, his sacrifice is not accepted as an Udh-hiyah.
Allaah Knows best.