Thank you for the question, “Did Zechariah go into the Holy of Holies?”
In Luke 1, the Scripture records these words, “ Once when Zechariah’s division was on duty and he was serving as priest before God, 9 he was chosen by lot, according to the custom of the priesthood, to go into the temple of the Lord and burn incense. 10 And when the time for the burning of incense came, all the assembled worshipers were praying outside. 11 Then an angel of the Lord appeared to him, standing at the right side of the altar of incense” (NIV).
Based on the text, Zechariah did not enter into the Holy of Holies. Only the High Priest can enter the Holy of Holies and that was once a year to make atonement for the Israelites. The High Priest at the time of Jesus was Annas.
John 18 says this, “Then the detachment of soldiers with its commander and the Jewish officials arrested Jesus. They bound him 13 and brought him first to Annas, who was the father-in-law of Caiaphas, the high priest that year. 14 Caiaphas was the one who had advised the Jewish leaders that it would be good if one man died for the people” (NIV).
Luke 1 says this, “The next day the rulers, the elders and the teachers of the law met in Jerusalem. 6 Annas the high priest was there, and so were Caiaphas, John, Alexander and others of the high priest’s family. 7 They had Peter and John brought before them and began to question them: “By what power or what name did you do this?” (NIV).
Thus Zechariah could not enter the Holy of Holies, but he could enter the Holy Place to burn incense. The Tabernacle was divided into the Holy Place and the Holy of Holies where by the Ark of the Covenant was placed behind the veil in the Holy of Holies. The Holy Place had the candlestick, the showbread, and the Altar of Incense. The incense altar was positioned directly in front of the veil leading to the Most Holy Place of the tabernacle. The lighting and offering of the incense on the Altar of Incense was a once in a lifetime opportunity.
Leviticus 40 says this, “Then the LORD said to Moses: 2 “Set up the tabernacle, the tent of meeting, on the first day of the first month. 3 Place the ark of the covenant law in it and shield the ark with the curtain. 4 Bring in the table and set out what belongs on it. Then bring in the lampstand and set up its lamps. 5 Place the gold altar of incense in front of the ark of the covenant law and put the curtain at the entrance to the tabernacle” (NIV).
Leviticus 16 says this, “2 The LORD said to Moses: “Tell your brother Aaron that he is not to come whenever he chooses into the Most Holy Place behind the curtain in front of the atonement cover on the ark, or else he will die. For I will appear in the cloud over the atonement cover” (NIV). In Leviticus 16, God states who can enter and the requirements for entering into the Holy of Holies.
SUMMARY: Zechariah enter the Holy Place to offer the incense on the Alar of Incense which was located in front of the curtain to the Ark of the Covenant. He didn’t enter the Holy of Holies.
For more perspectives:
https://www.quora.com/Did-Zechariah-go-into-the-Holy-of-Holies