Grief makes time feel endless in this short poem. The speaker is mourning a woman who has died. The poem never says who she was, so we can only judge from the closeness of the imagery that she mattered deeply. The opening "tick. tock." is broken into separate lines, as if each second is slow and heavy. The pendulum keeps swinging, but the day "would never end."
The speaker finds a small escape in closing their eyes and imagining her "laughing, breathing" nearby. That comfort doesn't last. Opening their eyes brings back the reality of her death, and the pain feels unavoidable.
The ending is the most striking part. "and / My / Eternity" is split into single words, so we're made to pause on each one. Eternity usually sounds grand, but here it means a life stretched out under sorrow. The mood is quiet, raw, and trapped.