What is the specific meaning of 時の函 in this song lyric?

Question

I came across a song (琥珀ト瑠璃ノ輪舞曲) where there's a line

"時の函に横たわっていた".

I know the meaning of the words individually ,

"時の" = of a certain time,
"函" = box,
"横たわる" = lying down /stretching out.

But putting them to together in the sentence makes no sense to me. The most literal way I can translate it is "Lying in a box of a certain time" But the meaning seems incomplete to me. Is there any other meaning behind it? Thank you!

For context, these are the song lines before it :

煤けた硝子玉 淡い月と碧い夜
それだけを映して時の函に横たわっていた

Answer 1

The literal translation is:

時の函に横たわっていた
[I] was lying in the box of time

Judging from the broader context, this is the author's own poetic way of saying "(I) have spent a long time lying in this box". This 函 primarily refers to the "frame of time", but I guess it's also a reference to a physical storage box. Note that the character ("I") in this song is a half-forgotten and half-broken windup doll who has been waiting for a new owner for a long time. 煤けた硝子玉 refers to his own glass eyes.