1. Question:

Is “day of” an idiomatic expression, meaning “general time”?

Why does Luke say the day of the Passover came, when it had not?

Is there any historical evidence, or grammatical rules, that may suggest that this phrase was often used imprecisely, idiomatically?

Then came the Day of: …
Then came the Feast of: …

Is it possible that: “It’s the Feast of Passover!” – may have have been understood the same way that we understand: “It’s Christmas Time!”, (a generalization, not necessarily the actual day);
Are Verb Tenses Significant? (“Then came:“, Aorist, Imperfect, etc.)
Are there any historical texts, that either confirm or refute this argument?

2. The Text:

NASB, Luke 22:1 – Now the Feast of Unleavened Bread, which is called the Passover, was approaching.

Day of Unleaven, (Mark 14:12, Luke 22:7)
Day of Preparation (Luke 23:54)
Feast of Passover, (Luke 2:41, John 13:1)
Day of Passover, (John 19:14, “Day” is elided)

Passover Came:

NASB, Luke 22:7 – Then came, (Ἦλθεν, Aorist Tense) the day

But It Had Not, Yet? :

NASB, Luke 23:17 – Now [Pilate] was obliged to release to them (at / κατὰ) the feast one prisoner.

John 19:31 – Then the Jews, because it was, (Imperfect Tense) the day of preparation, … for a Great Day was that Sabbath.

3. Research in Progress – Feel Free to Use:

Homilies on Matthew (Chrysostom), Homily 81 – And this one calls the day before the feast of unleavened bread, Luke 22:7 speaking of the time when they came to Him, and another says on this wise, Then came the day of unleavened bread, when the passover must be killed; by the word came, meaning this, it was near, it was at the doors, making mention plainly of that evening. For they began with the evening, wherefore also each adds, when the passover was killed.

Note: Although Augustine, (354-439) cited Chrysostom as an authority – I feel that what Chrysostom, (349-407) wrote is not conclusive because those works were not contemporaneous with the New Testament.