when

At what time? At which time? Upon which occasion or circumstance? Used to introduce direct or indirect questions about time.

• When will they arrive?
• Do you know when they arrived?
• I don't know when they arrived.

Used after a noun or noun phrase in isolation to express impatience with an anticipated future event.

• The site's all bugged. Fix when?
• Tank class buff when?
• My fridge even restocks itself these days. Glorious AI overlords when?

At an earlier time and under different, usually less favorable, circumstances.

• He's mister high and mighty now, but I remember him when.

At which, on which, during which: often omitted or replaced with that.

• That was the day when the Twin Towers fell.
• Not a week goes by when I don't mourn that loss.

The time at, on or during which.

• I recall when they were called the Greys.
• Next year is when we elect a new mayor.

A circumstance or situation in which.

• Love is when you can't get enough of someone.

At (or as soon as) that time that; at the (or any and every) time that; if.

• Pavlov's dogs salivate when [i.e. at any and every time that] they hear a bell.
• When [i.e. at any and every time that] he speaks to her, he is always polite.
• Put your pencil down when [i.e. as soon as, at the moment that] the timer goes off.

During the time that; at the time of the action of the following clause or participle phrase.

• They dream when [i.e. during the time that] they sleep.
• I'm happiest when [during the time that, or at any time that] I’m working.
• It was raining when I came yesterday.

At what time; at which time.

• I am here till Friday, when [i.e. at which time] I leave for Senegal.
• I was just walking down the street, when [i.e. at which time] all of a sudden it started to rain.

Since; given the fact that; considering that.

• I don't see the point of putting up Christmas decorations when I am the only person who is going to see them.

Whereas; although; at the same time as; in spite of the fact that.

• You're picking at your scabs when you should be letting them heal.
• He keeps changing things when the existing system works perfectly well.

What time; which time.

• Since when do I need your permission?

The time at which something happens.

• A good article will cover the who, the what, the when, the where, the why and the how.

That's enough: a command asking someone to stop adding something, especially an ingredient or portion of food or drink; used in, or as if in, literal response to 'Say when'.

Expressing impatience.