Hi willtor,
I don't 'disbelieve' it. I just disagree that the plain meaning of the text is what you say. So, if there's any disbelieving, it's that I 'disbelieve' you. For me, the plain meaning of the text is that to God a day that we know is as a thousand years and a thousand years that we know is just like a day to God.
You see, Peter was reflecting on and recounting what the psalmist had written:
For a thousand years in your sightare like a day that has just gone by, or like a watch in the night.
Further, even if one were to assume your position, that passage only addresses the word 'day' in the creation account. God gave several qualifiers as to what He meant us to understand as the length of time of the 'days of creation'. So, to accept your interpretation, then we have to throw out all the qualifiers and say, "Well, it uses the word 'day' and here's what Peter said about God's understanding of a 'day'.
But, God wrote the Scriptures for those He created to understand and He knew that this issue of 'what is a day' would come up because He knows that 'day' is one of those words that can have a few different meanings and He knew that the psalmist and Peter would one day write what they wrote. He also knows the beginning from the end and so He also knew that the time would come would men would not put up with sound doctrine, but rather fill their itching ears with what they wanted to hear. So, God put in the qualifiers so that men could read the creation account and understand that His use of the word 'day' here was not to be confused as some arbitrary length of time, but rather was defined as consisting on one evening and one morning.
God bless you.
In Christ, Ted