when???

Don’t let it escape your notice, dear friends, that with the Lord a single day is like a thousand years and a thousand years are like a single day. The Lord isn’t slow to keep his promise, as some think of slowness, but he is patient toward you, not wanting anyone to perish but all to change their hearts and lives. But the day of the Lord will come like a thief. On that day the heavens will pass away with a dreadful noise, the elements will be consumed by fire, and the earth and all the works done on it will be exposed. Since everything will be destroyed in this way, what sort of people ought you to be? You must live holy and godly lives, waiting for and hastening the coming day of God. Because of that day, the heavens will be destroyed by fire and the elements will melt away in the flames. But according to his promise we are waiting for a new heaven and a new earth, where righteousness is at home. (2 Peter 3:8-13, CEB)

Do not think God is slow or has missed your needs. To God, a day is like a thousand years and a thousand years is like a single day. God is patient and merciful, slow to anger, abounding in steadfast love, so that all might come to an understanding of the love God has for them.

So when will God come back?

That is really only for God to know. However, I think it is when we all get it and realize we need to love each other and bring the fulfillment of the kindom to earth.