Zevachim 56 - The Area for Slaughter, the Time for Blood
Peace offerings had to be slaughtered after the doors of the Temple Hall were opened; if they were slaughtered before that time, they were invalid, since the Torah said, "And he shall slaughter it at the entrance of the Tent of the Meeting" - at the time when one can enter, not when it is locked.
Most holy offerings must be eaten, and the peace offerings must be slaughtered "in front of the Tent of the Meeting." In order to make the whole area of the Courtyard "in front," there were additional doors, on the opposite far sides of the Hall, leading into the Hall.
The blood of the sacrifices had to be offered before sunset. After sunset it became disqualified, because of the verse " on the day that he offers his sacrifice it shall be eaten ." This teaches that both the slaughter and the offering of the blood must occur on the same day.
Art: Charles Théodore Frère - Sunset On The Nile