When eternity ends:

"Eternity" in the New Testament is generally translated from the Greek word "aionios" from the Greek word "aion"

When an author actually means "eternal" the Greek word "aidios" is used. (Romans 1:20) This aidios "eternal" never ends. Otherwise, if aion or aionios are used they do not mean eternal, but mean "for the age" (even though mistranslated as "eternal").

OLD TESTAMENT AGES

Leviticus 24:8 tells of the Mt. Sinai or Mosaic covenant as being an everlasting covenant yet Jeremiah 31:31 prophesies its end with a second and better covenant. Hebrews 8:7-13 reiterates this prophecy as being fulfilled. This seeming contradiction is solved by checking the Hebrew words of the inspired writers. We find in Leviticus 24:8 the word OLAM used instead of the erroneous word everlasting of the King James Version. The Sinai covenant lasted over 1500 years and was not an unlimited duration of time and was NOT everlasting.

Exodus 40:15 and Numbers 25:13 declare the Aaronic priesthood will be everlasting but this everlasting ended with the closing of the Sinai covenant to the Jewish nation.

The Word of Yahweh is proven to be sound and true - not a contradiction - by examining the Hebrew. The two mentioned scriptures reveal that the Aaronic priesthood is an OLAM priesthood (one that lasts for a definite period of time - an age) and not one that endures for an unending length of time.

Deuteronomy 23:3-5. The for ever in this scripture is self explanatory by its contents. It is a period of ten generations and the Hebrew word again is OLAM or AGE.

NEW TESTAMENT AGES

The New Testament uses the Greek word "AION" for "AGE".

Philemon 1:15
For perhaps he therefore departed for a season, that thou shouldest receive him for ever;

Paul is writing to Philemon, on behalf of Philemon's former servant, Onesimus. Paul is admonishing Philemon to accept Onesimus back again, not as a servant this time but as a brother in Christ. The for ever at the end of the sentence is an incorrect translation of the word "AIONIOS". With this meaning the sentence correctly reads that Philemon should accept Onesimus back for the duration of the AGE (a period of time) and not throughout all eternity.

Jude 1:7
Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire. Also read Genesis 19:24-29.

There are no ruins that remain on fire today as this scripture proclaims. Archaeologists have noted the most possible sites of these cities as being at the southern end of the Dead Sea. What then is amiss? By examining the text of the Greek manuscripts we find the word AIONIOS or AGE-LASTING in place of the word eternal of the King James Version. Now we have harmony of events. The cities were on fire and smoldered only during that Age or length of time that combustible materials remained to burn.

Revelation 19:3 "And again they said, Alleluia. And her smoke rose up for ever and ever." is mistranslated and actually means "for two ages" similar to a "time and times and the dividing of time." (Daniel 7:25).

When "eternity" or "everlasting" or "for ever" are translated from the Hebrew "olam" or the Greek "aion" they mean a period of time with a beginning and an end. There are still some Christians who mistakenly accept "eternal" hellfire as non-ending, literally, for ever. Actually it means "until the age". This is when "eternity" ends.