Blessings TMK,
It seems to me from reading Leviticus 16 that the High Priest enters the Holy of Holies at least twice on the Day of Atonement.
Lev 16:6 And Aaron shall offer his bullock of the sin offering, which is for himself, and make an atonement for himself, and for his house.
11 And Aaron shall bring the bullock of the sin offering, which is for himself, and shall make an atonement for himself, and for his house, and shall kill the bullock of the sin offering which is for himself:
12 And he shall take a censer full of burning coals of fire from off the altar before the Lord, and his hands full of sweet incense beaten small, and bring it within the vail:
After he is done with that he offers a goat for the sin of the people.
15 Then shall he kill the goat of the sin offering, that is for the people, and bring his blood within the vail, and do with that blood as he did with the blood of the bullock, and sprinkle it upon the mercy seat, and before the mercy seat:
I think the idea here is that only on the Day of Atonement the Priest can enter the Holy of Holies
Also expressed in these verses.
Lev 16: 1,2
And the Lord spake unto Moses after the death of the two sons of Aaron, when they offered before the Lord, and died;
2 And the Lord said unto Moses, Speak unto Aaron thy brother, that he come not at all times into the holy place within the vail before the mercy seat, which is upon the ark; that he die not: for I do appear in the cloud upon the mercy seat.