The reference to a thousand years being as one day with the Lord is in 2 Peter 3:8 and in context refers to the last days. This reference is highlighting how short human perspective of time is compared to God's perspective or all of time.
Time and terms for time have similar meanings in Genesis which starts before the Earth and Sun existed and the concept of a 24 hour day can have no meaning. A "day" in these contexts is simply a convenient and understandable term for a "cycle of time" or period of unknown duration. The http://english.answers.com/Greek term "aeon" is more accurate but would only be used in educated audiences. For the broadest audience the term "day" was sufficient to get the message across.
Every language including ancient Hebrew and Aramaic have colloquial terms for concepts of time that happen in everyday life and over the course of history.
A related example is "Forty days and forty nights", another symbolic or colloquial reference to a period of time. It is meant as "enough time to get the http://jobs.answers.com done" and comes from the period of time required to learn the Torah in preparation for Bar Mitzvah or the ritual of being tested and graduating from child to adult. This may be a few weeks or it may be several years. The colloquial term was and is used in the Middle East to mean "whatever time it took" or "whatever time it will take".
In the modern Carribean the term "Manyana" literally means tomorrow but universal common use has come to have Manyana mean "it happens when/if it happens". Travellers are often confused when they are told that something will happen "tomorrow" or "Manyana" when they were actually being told that "we aren't sure when or whether it will happen but we'll try to make it happen... chill out mon".
The Bible/Torah and much of Jesus's discussions were for common use and use the colloquial expressions of the times.
Time hasn't "shifted." Time is "physical"... computed by "the movements [orbits and rotations] of the planets." A 24-hour day is computed by the "rising of the sun" as viewed from a fixed point on earth... which is a 24-hour period composed of a "nighttime" period and a "daylight" period.
The biblical account is very clear on this:
"...He called the light 'daytime,' and the darkness 'nighttime.' TOGETHER THEY FORMED THE FIRST DAY." (Gen.1:4 LVB Living Bible)
Peter's "thousand year" comparison to one day, as mentioned above, is a "prophetic" reference to the 7000-year plan of God, which compares to a "7000-year, 7-day WEEK"... in which God is allowing man to "govern himself on earth" for his 6000 year, 6-day WORK WEEK.
"SIX DAYS shalt thou labour, and DO ALL THY WORK." (Ex.20:9)
The generations of men over the past five to six-thousand years and their continuously failed attempts to govern themselves apart from their Creator's laws, has been teaching them the erroneous and destructive ways of sin [disobedience to God's laws - I John 3:4].
Man doesn't realize this yet... but Judgment Day will bring all of life's lessons into full focus for everyone.
At the conclusion of this allotted 6000 years, God will intervene in world events, man's ERRANT, WICKED WORKS WILL CEASE [and his god, Satan will be banished]... and the "Lord's Rest" [Sabbath] will begin: the Thousand Year [7th day of the week] Rule of Christ on earth over the nations.
"But THE SEVENTH DAY IS THE SABBATH OF THE LORD THY GOD: IN IT THOU SHALT NOT DO ANY WORK..." (verse 10).
The works of sin will no longer be in vogue on earth during God's Thousand-year Sabbath Day.
"...I will write My Laws in their minds so that they will know what I want them to do without My even telling them, and these laws will be in their hearts so that they will want to obey them..." (Heb.8:10 LVB).
In the physical calculation of time... the days, months and years... THERE IS NO PHYSICAL REASON for the repetitive "seven-day week" to exist! Except that God set aside the seventh day of His "Divinely Inspired Creation Week" for man to REMEMBER CREATION... to REMEMBER THAT HE IS CREATED.
"REMEMBER THE SABBATH DAY, TO KEEP IT HOLY... For in six days THE LORD MADE HEAVEN AND EARTH, THE SEA, AND ALL THAT IN THEM IS, AND RESTED THE SEVENTH DAY..." (Ex.20:8 & 11)
The Divinely-Inspired seven-day week is for a weekly remembrance of God for man. A weekly renewal and reminder that he didn't "evolve," like this Satan-guided, Sabbath-forgetting, God-forgetting world teaches.
And the seven 24-hour day week is also a reminder to man of God's 7000-year, 7-day plan of Salvation and Redemption and Release from sin... and the god he chose to worship in the beginning.
Time never "shifted." God set the earth revolving in 24-hour rotations from the first day. And the knowledge of His prophetic 7000 year, 7-day week plan of Salvation has been revealed to His servants, now, at the time of the end of man's allotted "6000-year-day work-week." Like clockwork, it's all right on schedule.