Against the clock
Definition 1 of 2
Pro Tip 1/3Urgency Emphasis
Used to highlight urgency when time is a critical factor in completing a task. 
With the deadline approaching, we were against the clock to finalize the report.
Pro Tip 2/3No Literal Clock
The clock is metaphorical, meaning simply that time is limited, not an actual race against a timepiece. 
She was against the clock to finish her essay by midnight.
Pro Tip 3/3High Pressure
The phrase adds a sense of tension or pressure to the situation. 
The emergency team worked against the clock to save the injured climbers.