Expression of numbers and frequency in English

Example: The minimum temperature in Greece yesterday was 15ºC and the maximum temperature was 30ºC.

To express the idea of the largest amount possible, we normally use maximum. Minimum describes the smallest amount possible.

Example: I play tennis once a week.

When something happens at one point within a period of time we normally use once.

Example: He had only seen his great-aunt once before.

He had only seen his great-aunt one time before

One time is occasionally possible as an alternative to once.