This phrase is often used to describe a situation where time is of the essence. It is a warning that time is running out and that action must be taken quickly. In this case, it is a reminder to stay focused and take action before it is too late.
From Wikipedia
A clock or chronometer is a device that measures and displays time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia.