at 用于时间时，除用于 at 5 o'clock 这类搭配外，还有其他一些用法。比如：

1. 用于年龄。如：

He plans to retire at (age) 65. 他计划65岁退休。

The athlete reached the summit of his prowess at the age of thirty. 这位运动员在30岁时技术达到顶点。

2. 用于短的假期。如：

Business is good at Christmas when people buy presents. 圣诞节人们买礼品，生意兴隆。

We'll probably go away at Easter. 复活节我们可能要外出度假。

3. 用于某些固定搭配。如：

That is the exact price at the moment. 那是目前精确的价格了。

His attitude wasn’t yet very definite at that time. 他的态度当时还不很明确。

There isn’t much fruit on the market at this time of year. 每年这个时候水果供应不多。

其实，你的问题随便找本词典查一下都可以解决的。