Read 2 Pet. 3:8, in its entirety, and you will see that it says something quite different: “with the Lord one day is as a thousand years, and a thousand years as one day.” It doesn’t say “one day is a thousand years,” but that one day is “as” (like) a thousand years. Then it also says the reverse: a thousand years is “as” (like) one day. So that alone negates the idea of a different timescale. The verse is saying that both times are equivalent. In addition, it is not comparing God’s timeframe to man’s. Rather, both times are from God’s perspective: “with the Lord” these times are the same. Scripture is telling us that with God time has no meaning. Because He is eternal, outside of the dimension of time that He created, a million years, a day, and a millisecond all are the same to Him. He sees all of history simultaneously.
Genesis 1:31 Then God saw everything that He had made, and indeed it was very good. So the evening and the morning were the sixth day.