Psalms 90:1-4: Lord, You have been our dwelling place in all generations.
2 Before the mountains were brought forth,
Or ever You had formed the earth and the world,
Even from everlasting to everlasting, You are God.
​ 3 You turn man to destruction,
And say, “Return, O children of men.”
4 For a thousand years in Your sight
Are like yesterday when it is past,
And like a watch in the night.
5 You carry them away like a flood;

God actually inhabits eternity (Isaiah 57:15). That is, just as men inhabit or live on earth, God lives in eternity. This is, of course, a realm above and beyond time and space. It would be a mistake to try to understand eternity by time. Someone suggested that eternity is time with both ends knocked out, but eternity is actually something quite apart from time. Eternity is not just a long, long time. It is apparently more a state of being. Perhaps one way to think of it is as the "eternal present." 

Lord - Not יהוה Yahweh here, but אדני 'Adonāy. The word is properly rendered "Lord," but it is a term which is often applied to God. It indicates, however, nothing in regard to his character or attributes except that he is a "Ruler or Governor."
Thou hast been our dwelling-place - The Septuagint renders this, "refuge" - καταφυγἡ kataphugē. So the Latin Vulgate, "refugium;" and Luther, "Zuflucht." The Hebrew word - מעון mâ‛ôn - means properly a habitation, a dwelling, as of God in his temple, Psalm 26:8; heaven, Psalm 68:5; Deuteronomy 26:15. It also means a den or lair for wild beasts, Nahum 2:12; Jeremiah 9:11. But here the idea seems to be, as in the Septuagint, Vulgate, and Luther, "a refuge"; a place to which one may come as to his home, as one does from a journey; from wandering; from toil; from danger: a place to which such a one naturally resorts, which he loves, and where he feels that he may rest secure. The idea is, that a friend of God has that feeling in respect to Him, which one has toward his own home - his abode - the place which he loves and calls his own.
In all generations - Margin, "generation and generation." That is, A succeeding generation has found him to be the same as the previous generation had. He was unchanged, though the successive generations of men passed away.
​--Barnes Notes on the Bible 

The first verse expresses confidence in God as the source of protection and care. “Dwelling place” is closely related to the term “refuge” which appears frequently in the Psalms (2:12; 34:8; 71:3). The claim about God here is very personal— the Lord is “our dwelling place” (italics added). The concern for time is also apparent from the start. The Lord has been our dwelling place “in all generations.” Verse 2, however, declares God’s greatness by pointing to God’s time. Before the world was put in order God was God.  --Ministry Matters