据我所知，彼得一生中几乎只有这一次感到害怕。

For almost the only time in his life that I know of, Peter was afraid.

youdao

只有这一次他按时到了。

Just for once he arrived on time.

《牛津词典》

只有这一次不同：我是那个说“不”的人。

Except this time there was one difference: I was the one saying no.

youdao

A couple of hours, because typically there's just one battle; one side beats the other and that's the war for now.

几个小时,一般来说只有一次战斗,一方攻打另一方,这就是战争

耶鲁公开课 - 古希腊历史简介课程节选

And then other people are really excited because it's a once-in-a-lifetime opportunity

而另外一些人真的很兴奋，因为这是一个一生只有一次的机会，

正准备奥运会 - SpeakingMax英语口语达人