Exploring when is the 6000 years start within the Gregorian calendar.

Matt. 24:36 But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only.

Rev. 20:4 And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.

For more information refer to https://heavenscatalyst.org/truth/revelation-commentary/