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?