Wiktionary
tick down
vb. (context of a clock or other timer English) To count the time down to zero.
Usage examples of "tick down".
She brooded over the plot, watching the clock tick down, and bit her lip, hating herself for what she had no option but to do.
Honor watched the chronometer tick down, and her mind was cold and clear, accepting no possibility of failure.
She cradled Lisa against her chest and stared across at the clock on the wall, watching the time tick down.
And finally, humans stood within the OnOff system, and watched the seconds tick down toward a new Relighting.
The time remaining continued to tick down steadily, second by second.