against反对、针对，against the clock真实含义是争分夺秒，分秒必争。

【例句】
The emergency services were working against the clock as the tide began to rise.
开始涨潮了，紧急救援机构正在争分夺秒地工作。

It's now become a race against the clock.
从现在开始要分秒必争，跟时间赛跑。