According to Seventh Day Advent theology when does the 2300 evenings and mornings in Daniel 8:13-14 begin? Daniel 8:13-14 NIV

13 Then I heard a holy one speaking, and another holy one said to him, “How long will it take for the vision to be fulfilled—the vision concerning the daily sacrifice, the rebellion that causes desolation, the surrender of the sanctuary and the trampling underfoot of the Lord’s people?”
14 He said to me, “It will take 2,300 evenings and mornings; then the sanctuary will be reconsecrated.”

I have heard that according to SDA theology that the 2300 evenings and mornings began in 457BC and have been interpreted as years instead of days
My question is how they get to this date?
According to SDA theology, 457 B.C. is the beginning of the 70 weeks prophecy.  The prophecy of Daniel 9:25 was fulfilled in 457 B.C. when Artaxerxes authorized Ezra through a royal decree to go to Jerusalem accompanied by a group of exiles to restore and rebuild the city.  The document below presents historical evidence to support the validity of 457 B.C.  Source: https://www.adventistbiblicalresearch.org/materials/prophecy/70-weeks-and-457-bc  Copyright © Biblical Research Institute General Conference of Seventh-day Adventists®
As I understand it, the principal that one day equals one year in prophetic language is based on the following Scriptures:

According to the number of the days in which you spied out the land, forty days, for each day you shall bear your guilt one year, namely forty years (Numbers 14:34 NKJV).
I have appointed thee each day for a year (Ezekiel 4:6).

On the basis that one day equals one year, then the 70 weeks equate to 490 days or 490 years.  490 years from 457 B.C. brings us to the baptism and ministry of Jesus, the Messiah.

Seventy weeks are determined upon thy people and upon thy holy city, to finish the transgression, and to make an end of sins, and to make reconciliation for iniquity, and to bring in everlasting righteousness, and to seal up the vision and prophecy, and to anoint the most Holy (Daniel 9:24).

“Thy people” were God’s chosen people Israel. Seventy weeks resolves into 490 days. Applying the day-year principle, 490 days become 490 years.
There follows another prophetic “week” from the baptism of Jesus, as the Messiah, to his crucifixion, the pouring out of the Holy Spirit at Pentecost when the Gospel was then taken to the Gentile nations, culminating in 70 A.D. when the Romans destroyed the Temple in Jerusalem.  More information here on the Seventh-day Adventist prophetic time chart regarding the prophecies of Daniel and Revelation: https://en.wikipedia.org/wiki/Seventh-day_Adventist_theology#/media/File:Adventist_1863_chart.jpg
Please note I am NOT a Seventh Day Adventists, but I have done my best to find reliable sources of information in an attempt to answer your question.