Meaning of "And the day came when ... "

I saw some sentences that start with this phrase: "And the day came when ... " For example, the following sentence form The Garden Party and Other Stories by Katherine Mansfield

At last the day came when everyone except the Kelveys had seen the doll's house.

What does it mean?

Solution 1:

This is a sentence which uses extraposition from noun phrase movement. Often when a noun phrase (NP) has a long relative clause, or other modifier, that modifier gets moved out of the noun phrase and appears at the end of the sentence. This is particularly likely when the rest of verb phrase is very short (here it is just last week). Here is another example:

• We fired three people last week who had been stealing parrots.

In the sentence above, the phrase who had been stealing parrots has been moved to the end of the sentence. The canonical word order would be:

• We fired [three people who had been stealing parrots] last week.

The longer the modifier and the shorter the verb phrase the more likely this is to happen. It very often happens, therefore, with intransitive verbs like COME.

• An inspector came in from the Inland Revenue.

Notice that the sentence above probably does not mean that they came in from the Inland Revenue!

The Original Poster's sentence

At last the day came when everyone except the Kelveys had seen the doll's house.

The Original Poster's sentence is slightly confusing because of the non-canonical word order. Part of the subject phrase has been moved to the end of the sentence. If we keep the subject intact, as one phrase, we get:

• At last [the day when everyone except the Kelveys had seen the doll's house] came.

Although this is the canonical word order, it is a bit clumsy because the subject is so long. It is, however, easier to see how the grammar works!

Note: In case you want to Google it, extraposition from noun phrase movement is often written: extraposition from NP

Solution 2:

A day is unit of time:

noun

1 A period of twenty-four hours as a unit of time, reckoned from one midnight to the next, corresponding to a rotation of the earth on its axis.

_ODO

We often speak of time metaphorically in terms of spacial movement as in:

• the time has come
• take each day as it comes
• the day is coming

The expression the day came has a long illustrious history in English literature:

• From the 1548 publication of Edward Halle's The Union of the Two Noble and Illustre Famelies of Lancastre and Yorke:
  And lo whan the day came ti every thing was redy, he was crowned Emperor in the churhe of Öazhetecan in the citie of Bottom by pope Clemet the vii

• From the 1553 publication of The Newe Testament in Englishe Translated After the Greke:
  And the child grew and wexed strang in sprite, he was in wildernes til the day came, whe he would shew himself unto the Israelites.

• From the 1611 publication of The King James Version of the Bible:
  Whenever the day came for Elkanah to sacrifice, he would give portions of the meat to his wife Peninnah and to all her sons and daughters.

• From The First Sketch of Shakespeare's Merry Wives of Windsor:
  Genobbia wondered much at this, as she had done before: but, ... she did what he had commanded her; and, when the day came, went to the church richly clad

• From the 1838 publication of Charles Dickens' Nicholas Nickleby:
  The sluggish darkness thickened as the day came on

• From the 1999 publication of Salman Rushdie's novel, The Ground Beneath Her Feet:
  Vina, who had seen too many things in her short life, was less tight-lipped, and the day came when she could stand it no longer.

emphasis added

Conclusion:

The expression the day came can be a simple metaphoric expression of time indicating that a particular day has arrived. It can also be used as a metonym of any particular point in time. In the OP, the example sentence seems to indicate that it was just a matter of time until everyone would see the doll house:

At last the day came when everyone except the Kelveys had seen the doll's house.

Eventually, everyone had seen the doll house except for the Kelvey's

Solution 3:

Assuming @webbcode is correct, the following sentence would read:

At last the day came when everyone except the Kelveys had seen the doll's house.

This means: Now everyone except the Kelveys had seen the doll's house.

The reason "At last, the day came when..." is used is for dramatic impact. It creates a sense of importance to the event, whereas "Now..." is rather abrupt and mundane.