2 Peter 3:8 But, beloved, do not forget this one thing, that with the Lord one day is as a thousand years, and a thousand years as one day.

A great truth!
In context to which the apostle gave it, he is still taking on the scoffers about the return of the Lord.
Those scoffers would say so much time has passed with no sign of the Lord, perhaps the time for His coming is expired.
There is no expiration date with God.
Time does not matter.
Nothing is long and nothing is short.
Whether it takes a day or a thousand years for His purpose and plan makes no difference to Him.
For you and me, the longer it takes for Him to return, the more opportunity for us to spread the Gospel and the more time for others to accept it.
But, as in the days of Noah, time ends.

Another possibility I’ve heard deals with our time as a whole.
God created everything in six days making the seventh a holy day of rest.
Was each day a thousand years?
I don’t believe so since Adam was created on the sixth day and God interacted with him after the seventh day.
But Adam only lived 930 years, which is 70 years short of a thousand so Adam never lived to the seventh day or the next thousand years.
Scrap that idea.
I’ve also heard that every thousand years is equal to one of the days of creation. Meaning, if the earth is around 6,000 years old then the last millennium is the one in which Christ shall reign.
And we are getting extremely close to the end of the sixth millennium.