........was the original garden a temporal state or was it eternal in its nature before the fall?
I believe the scriptures are very clear that the garden of Eden was on this present earth and everything on this earth experiences time as well as on the new earth to come according to scripture.
God created time to enable His creation to function sequentially. He pronounced it very good and there is no reason to believe He has changed His mind.
Its commonly believed that Heaven will be a realm outside of time; timeless.
Although it is commonly believed - it is definitely incorrect.
Whether you consider eternity to be spent on a new earth or in Heaven itself. There will be time experienced by us either way.
For instance:
The tree of life on the new earth yields its fruit every month. Revelation 22:2
"From one New Moon to another and from one Sabbath to another, all mankind will come and bow down before me". Is. 66:22-23
The book of Revelation shows the inhabitants of Heaven operating sequentially within time.
There is music and song in Heaven which require meter, tempo, and rest. Songs have a beginning, a middle and an end. Certain notes are held longer than others.
Heaven's inhabitants track in time down to rejoicing the moment a person
repents.
"there was silence in heaven for about half and hour." Rev. 8:1
"Summer and winter, day and night will never cease." Genesis 8:22
God's people "serve Him day and night in His temple." Revelation 7:15
The nations "bring" their gifts to the New Jerusalem. That requires moving from one place to another which involves time.
The Bible speaks of the "coming ages". Ephesians 2:7
The martyrs in Heaven are told to "wait a little longer" when they ask "how long " until Christ judges the earth and avenges their blood.
And on and on it goes.
There is absolutely no reason not to believe that what God pronounced very good will cease to exist in the world to come.
The omnipresent creator of this world obviously exists and functions in the time He created right along with His creation.
No doubt God Himself is not bound by time and He experiences time in a different way than we do. But even He experiences and functions in time as stated in various ways in the scriptures.