Brother Andrew,

Indeed, let us follow the book of Hebrews carefully (said in deep, affected, pastoral tones).

"According to the elaborate analogy that is being developed Jesus becomes a high priest at the resurrection. This is apparent from 5:5-10; 6:20; 7:15-16, 20-21, and the allusions to Psalms 2 and 110."

Andrew, you cannot force a wedge here, arguing that he only becomes a high priest (and thus enacts the ministry of a priest) at the resurrection, as though the cross that precedes it has little or nothing to do with his priestly ministry, where the author of Hebrews sees a seamless continuity.  Rather, from his incarnation, the author of Hebrews argues, through what he suffered on earth, and, culminating in his death on the cross, he became the perfect source of salvation for all who believe on him (5:9; cf. 10:14).  Because of his temptations on earth, for example, he is a sympathetic high priest who understands our weaknesses (He.2:10-18).  And through the obedience learned in what he suffered he is made perfect as a priest who atones and intercedes efficaciously for his people.

You are correct in noting that psalm 2 and 110 are messianic enthronement psalms, and speak of his ‘coronation’, if you will (cf. He.2:9).  He is certainly crowned as the conquering one, the victorious Messiah who has been ‘installed on Zion’, and concerning his priesthood (of the order of Melchizedek), it speaks of his having finished the work of atonement. Thus, "when this priest had offered for all time one sacrifice for sins, he sat down at the right hand of God," He.10:27.  Note, he was a priest when he offered his sacrifice for sins, which was clearly his death on the cross (1:3).  For "He sacrificed for their sins once for all when he offered himself," 7:27.  

So let’s follow this carefully: He sacrificed for sins WHEN He offered Himself.  When did He do this? When did He ‘put away sin by the sacrifice of Himself’?  When did he execute the ‘sacrifice of Himself’?  When did he offer up himself (note again the passive or reflexive voice here) for sins?  On what basis did he enter the holy place, but by his own blood (He.9:12; cf.9:14; 13:12)?  And where was His blood shed? 

Thus 9:26 speaks not of His entering the heavenly tabernacle, as you say, but His sacrifice on Calvary, on the basis of which He enters the true temple of heaven.  Sacrifice is done outside the camp, and the blood then brought inside the Most Holy Place (as you note, and see 13:12-13).  "He appeared once for all to do away with sin by the sacrifice of himself."  This ‘sacrifice of Himself’ clearly took place on earth, "outside the campe". Hence, otherwise "he would have needed to suffer often since the foundation of the world", v.26b, a suffering that clearly was/would be ‘terrestrial’.  

Nevertheless v.28 is clear: Christ ‘was sacrificed’ (NIV), or "having been offered" (NAS) - note again that this is NOT the act of the priest entering the tabernacle, it is rather acted upon the victim which is being sacrificed outside the Most Holy Place! - once "to take away the sins of the people." 

It seems you’re mixing your metaphors, my friend.  A priest does not enter the Most Holy Place to be offered (passive) for sins; rather he offers (active) blood not his own (9:25).  Jesus is presented in Hebrews though as both high priest and sacrifice.  You are only factoring his active priestly role into his royal priesthood, when in fact this priest passively/reflexively offered up himself on the altar as it were, a death that took place outside the camp (where in laying down his life, he was simultanously acting as priest and [acted upon as] victim).

Offering, btw, speaks not just of the act of bringing the sacrificial blood into the tabernacle but also the act of sacrifice itself (e.g., as in the case of Abraham ‘offering up’ Isaac on the altar). 

His appearance at the ‘end of the age’ then clearly speaks of His earthly ‘humiliation’.  Thus He.1:1-2 says: "In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son," and so on. His appearance in the last days (in the fullness of time) speaks of his ‘manifestation’ on earth in the first advent. 

Your demand that his priesthood was limited to His post-resurrection existence is too artificial and rigid for the robust, living theology of the NT, where, despite the clear link of resurrection to Ps.2 and 110 in Acts 13:33 and elsewhere, Jesus is nevertheless rightly called ‘Lord’ before His ascension (even before His birth, Lk.1:43), He is still identified as the Messiah before His resurrection from the dead (Mt.16:16), and declared by the heavenly Majesty to be ‘My Son’ before He sat down at the right hand as King (Mt.3:17; 17:5), indeed His ‘only-begotten’ glory was revealed throughout His earthly ministry (Jn.1:14).  

Jesus’ resurrection did not constitue His messianic identity, it did not even ‘anoint’ Him for His messianic ministry (Lk.3:21-22; 4:14-21; the performance of which revealed His identity, for those with eyes to see Lk.7:20-23), but declared Him to be the Son of God, the Messiah in power (in contrast to the so-called messianic secret of his earlier career, e.g., Mt.16:20). 

It is not without good reason then that tradition has titled John 17 as the high priestly prayer, where Jesus acts as intercessor, even sancitfying himself (no doubt for the impending events) for the sake of his disciples.  Jesus’ whole ministry, from one perspective, was a priestly ministry, a ‘making perfect’ of his high priestly role as atonement and intercessor for men and women. 

"But the writer then says that there will be a second appearance in the sanctuary,"

It is clear from the grammar and context that the second appearance is not in the sanctuary of heaven.  If you’re going to continue to insist on this interpretation, you still must explain how it is that Jesus sacrifices himself in heaven (not merely offers his blood, which is an active work of the priestly service), per your reading of Heb.9.

"This is clearly a salvation that those waiting do not yet have: an ending to their suffering and uncertainty."

And the receiving of an eternal kingdom that transcends the created order, a kingdom revealed in the cataclysmic ‘shaking of heaven and earth’ (He.12:26-28; cf. 1:11-12), and the world to come subjected to a redeemed humanity (He.2:5-9).  "Has this happened yet?", asks Captain Obvious.  Or do you limit the ‘people of God’ for whom the Sabbath-rest is yet future (at that point anyway) to the martyrs of the faith (He.4:9)?