What do you call a day that never comes?

Searching on Google Books I discovered that 'a day that never comes' has 2.060 results.

As an example usage, among a lot of others, in 'Healing Words' by Susan Brozek it is written:

If we wait until we feel like obeying, we will be waiting for a day that never comes!

I would like to know whether there is a short phrase or expression to refer to a day that never comes.

I focused my attention on 'a never day', but, checking for this phrase, I didn't found anything confirming it is a common usage.

Thus, what do you call a day that never comes?

Solution 1:

The commonest idiomatic phrase for this is

When Hell freezes over.

I have to say I loved @Wayfaring Stranger's when Godot gets here but I doubt it will be widely understood. I often use the 30th of February but it is not an idiomatic phrase as such.

Solution 2:

English has a term:

"epagomenal"

e.g. an epagomenal day. It's an adjective, though – from the Greek root epagein.

It refers to a "day out of time". We mostly use it to mean an intercalation day, but its origin is regarding a mythic day that does not and cannot occur in the time we experience. These were days reserved for gods and the like, and as such those days never did come for mortals.

I have heard speakers of Español use the word "Mañana" in this way.

it is not the only way to use 'mañana' - the word's most-basic meaning is 'tomorrow'. But there is a sad usage of it in this way — said with longing — that expresses that suggests the idea that tomorrow will never come. It is implied or inferenced in many contexts.

When will my suffering end? Mañana, my friend. Mañana....

It's the best fit for what you're looking for, I think.

Pardon that's not an English answer.

Solution 3:

Tomorrow never comes

Prov. When the day arrives that you are now calling "tomorrow," you will call that day "today" and a different day will be called "tomorrow." (Therefore, you should not resolve to do something tomorrow, since that day will never arrive.) Jill: When are you going to go to lunch with me? Jane: Tomorrow. Jill: Tomorrow never comes.

This is a very common idiom, apparently American in origin (the Freedictionary).