In Revelation the Bible describes the Millennium occurring after Armageddon.
Before Armageddon, Revelation describes Jesus as “now have come to pass…the kingdom..” so Jesus rulership begins before Armageddon. How long Jesus rules before Armageddon is a good guess.
After Armageddon, Revelation describes the Millennium as 1000 years in length assuming it means a solar year times a thousand and a thousand literarily means the quantity 1000. Can we be sure that the “Millennium” is literally 1000 solar years long with the book of Revelation describing itself as being symbolic? Let me know. Also don’t confuse believing with knowing.