10 But the day of the Lord will come as a thief in the night, in which the heavens will pass away with a great noise, and the elements will melt with fervent heat; both the earth and the works that are in it will be burned up.The “day of the Lord” is the Second Coming. One thing that will happen on that day is the passing away of this present heavens and earth, melting with fervent heat.
11 Therefore, since all these things will be dissolved, what manner of persons ought you to be in holy conduct and godliness,
12 looking for and hastening the coming of the day of God, because of which the heavens will be dissolved, being on fire, and the elements will melt with fervent heat? (2 Peter 3)
It is also the day of destruction and judgment for the unrighteous.
2 For you yourselves know perfectly that the day of the Lord so comes as a thief in the night.
3 For when they say, "Peace and safety!" then sudden destruction comes upon them, as labor pains upon a pregnant woman. And they shall not escape.
4 But you, brethren, are not in darkness, so that this Day should overtake you as a thief. (1 Thess. 5; cf 2 Peter 2:6-9)
I figure the ‘day of the Lord’ refers to the Millenial Kingdom that begins with the Second Coming in Rev 19 and the ‘battle’ of Armageddon followed by the 1,000 year reign (the Sabbath of the Earth - Rev 20). That is why there is the reference to the ‘thousand years is as a day’ in those verses in 2 Peter. It appears to be a clue that the ‘day of the Lord’ is 1,000 years long. At the end of that ‘day’, the heavens pass away, the earth is burned up in Rev 20:11 and the judgement begins followed by the new heavens, the new earth and the New Jerusalem.
Otherwise, it looks like 2 Peter is saying that the Second Coming doesn’t happen until Rev 20:11 and that is too late for the martyrs to reign w/ Christ during the Millenial Reign and the 1,000 year Sabbath of the Earth.