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


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




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](https://utaten.com/lyric/mi18112254/), 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.




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](https://utaten.com/lyric/mi18112254/), 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.

