This translation introduces an impossibility due to the fact that God's instructions to Israel plainly state that Passover is the day before the Feast of Unleavened Bread—and we can be sure that Christ and the disciples were not late! That the disciples inquired about making preparations—and later that night assumed Judas would be purchasing something "for the feast" (John 13:29)—shows that the time in question could not have been the first day of the Feast of Unleavened Bread. Why? That day is a holy convocation on which no customary work is to be done (Leviticus 23:7), if God's instructions are to remain unbroken.
So how are we to understand this verse? First, notice that the words "day of the Feast of" are italicized, showing that the translators added them to the text. The Greek literally reads, "And on the first unleavened. . . ." The word translated as "first," protos, typically signifies a thing that is first in a sequence or first in prominence. However, it can also indicate an order of events, as well as whether an event occurs before or concurrently with another.
For example, in John 1:15 John the Baptist acknowledges Christ's pre-existence, saying, "He who comes after me is preferred before [above] me, for He was before [protos] me" (see also verse 30). Also, in II Peter 2:20, Peter says of those who become entangled in the world again, "the latter end is worse for them than the beginning [protos]," again showing an order of events.
Matthew 26:17, then, can more accurately be translated, "Now before [the Feast of] Unleavened Bread the disciples came to Jesus, saying to Him, 'Where do You want us to prepare for You to eat the Passover?'" In other words, this incident happened before the Feast of Unleavened Bread had begun. Since they were inquiring about preparing the Passover, this could have taken place either late in the day on Abib 13 or possibly just after sunset on Abib 14 (since the Passover lamb was to be killed between sunset and dark as the 14th began).
David C. Grabbe