At even. See on Exodus 12:6. According to all the rites of it, and according to all the ceremonies thereof. This must be understood only of the essential rites and ceremonies of the passover, as mentioned below (Exodus 12:11, Exodus 12:12).
It is singular that no mention is made of the considerable departure which circumstances necessitated from the original institution. It was not possible, e.g; to strike the blood of the lamb upon the lintel and the side-posts of the doors, because in the wilderness they had no doors.
In after ages this rite (which was of the essence of the institution) was represented by the sprinkling of the blood of the lambs on the altar (2 Chronicles 30:16), but no command is on record which expressly authorized the change.
In Le Exodus 17:3-6 there is indeed a general direction, applying apparently to all domestic animals slain for food, that they be brought to the tabernacle to be slain, and that the priest sprinkle the blood upon the altar; and in Deuteronomy 16:5-7 there is an order that in future times the passover was only to he slain at the place which the Lord should choose.
The actual practice in later ages seems to have been founded partly upon the command in Deuteronomy, which restricted the killing of the passover to Jerusalem (not, however, to the temple), and partly on the command in Leviticus, which really applied (at any rate in the letter) to the time of wandering only.
As the celebration of the paschal feast had apparently been neglected from the time of Joshua until that of the later kings (Joshua 5:10; 2 Kings 23:22), they were no doubt guided in the observance of it by the analogy of other sacrifices in the absence of express commands.
It would, however, be an obvious source of error to assume that the practice of the age of Josiah or Hezekiah was the practice of the earliest passovers; so far as these necessarily differed from the original institution, it is absolutely uncertain how the difficulty was solved.
Nothing perhaps better illustrates the mingled rigidity and elasticity of the Divine ordinances than the observance of the passover, in which so much of changed detail was united with so real and so unvarying a uniformity.