在 meaning “When”

Question

The following sentence uses 在 in a way I haven't seen until now:

“在你走以前我们要给你开一个宴会。”

I roughly translated it as: "Before you go, we are going to give you a banquet", which I feel is a good enough translation.

However, I don't understand why the author uses 在 in this sentence, as I learned that 在 indicates a place, or marks an ongoing action, not some action that will still occur.

Answer 1

在 implies "at that time" [When?] "before you leave" - 你走以前. 在 modify the phrase 你走以前.

在我回來之前 你最好已離去 - You have better left already [When?] before I come back.

在秋冬交接之際 很容易感冒 - It's fairly easy to catch a cold [When?] during the change from Fall to Winter.

The words "從", "自", "打" can form a sentence in the same pattern to imply

從/自/打妳離我而去那日起 我就決定重新開始了/改變自己了. - I've made up my mind to have a fresh start/to change myself [When?] since the day you left me.

Answer 2

"在" as an adverb indicates an ongoing action.

But as a preposition it can indicate not only a place, but also time, scope, condition, etc.

In the sentence "在你走以前我们要给你开一个宴会”, it indicates time.

One more example of 在 indicating time (from 《现代汉语词典》):

事情发生在去年。