Single-Word Requests – What is the Spatial Equivalent of ‘Anachronism’?

Eternal does not refer to the "end of time." Eternal means "outside of time."

See Oxford

1Lasting or existing forever; without end or beginning:

Something that has existed "since forever" is eternal. It is outside of time and did not have a beginning.

Consider the cosmos. If it did not have a beginning, but has always existed, then it is eternal. If it had a beginning, it has not existed forever.

As an adjective, it would be used like: "My love for you is ...". The noun could be used like: "I have loved you since ...".

Adjective: eternal. My love for you is eternal.

Noun: Does not compute. You cannot use a 'time-word' such as "since" to refer to the eternal or eternity. However, you may simply replace "since" with "for". "I have loved you for eternity."

You can refer to "the beginning of time". "In the beginning, God created...", or "In the beginning, the Uncaused Cause caused...". On the other hand, you can't refer to "(Before) the beginning of time", because time came into existence along with the cosmos. Outside of time stands eternity.

Interstice:

a space that intervenes between things; especially : one between closely spaced things. Eg, interstices of a wall