clock是时钟，against the clock含义是“与时间赛跑；抢时间；争分夺秒”。

【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。

Doctors raced against the clock to save his life.
医生们争分夺秒地抢救他的生命。