The beginning of class is the latest possible time.

开课是最晚的时间。

So, " by" is a deadline; the latest time he can call me.

所以，“by”是截止日期；他可以给我打电话的最晚时间。

The word by means that we're talking about the latest possible time.

这个词的意思是我们正在谈论最新的可能时间。

The latest time you can meet me is just before noon because I'm leaving at noon. Right?

你最晚能见到我的时间是中午之前， 因为我中午要走。 正确的？

When we say we are going to do something at the last minute, we mean at the latest possible time before something happens.

当我们说我们要在最后一刻做某事时，我们的意思是在事情发生之前的最晚可能时间。