First, thank you for your question.

We should begin with verse 26 of Hebrews 9 "…but once in (the) end of the world to put away sin by the sacrifice of himself hath he appeared". This of course is referring to his death. "hath he appeared" - Phaneroo (Strong’s # 5319) means to "render apparent" or to "manifestly declare".

He hath in his death rendered apparent or manifestly declared sin to be put away and the old covenant world to be ended. This he did answering verse 27.

The appointed death of mankind (Adam) and the consequent judgment of the world—see John 12:31-33

Verse 28 refers to both His sacrifice (death) and His resurrection. "…second without sin shall he appear unto them that look for him unto salvation."

It is obvious that his appearing is not based on or governed by some future point in time or some future dispensation but rather is upon the condition—"unto them who look for him unto salvation by faith". This appearing is future only in relation to His appearing to put away sin. First He dies, then shall He live.

The actual phrase "shall he appear" is - Optanomai (Strong’s # 3700) meaning "to look at" or "to allow oneself to be seen". By whom shall he "be seen" as salvation? By those who believe on Him.