1
general::
Also, every moment counts. Time is of the essence. For example, Hurry up with those tools? every minute counts, or In performing surgery every moment counts. This idiom uses count in the sense of "to enter into the reckoning" (and hence be important).
American Heritage Idioms
2
general::
Phrase(s): Every minute counts. [and] Every moment counts.
Fig. time is very important. (Used especially in situations where time is very limited.) • Doctor, please try to get here quickly. Every minute counts. • When you take a test, you must work rapidly because every minute counts. • When you’re trying to meet a deadline, every moment counts.
McGrawhill's American Idioms And Phrasal Verbs