Learn a new idiom: against the clock

To do something against the clock is to do it very fast because you know you only have a limited period of time to finish it.

EXAMPLES

Boy: "Mom, will you have time to help me with my homework today?"
Mother: "Sorry, I won't. I'll be working against the clock to finish my presentation."

The City Council is racing against the clock to have everything ready for the visit of the Prime Minister on Saturday.