The theory of expansion indicates that the universe is expanding.

The model describes how the universe expandedfrom a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large scale structure and Hubble’s law. If the known laws of physics are extrapolated to the highest density regime, the result is a singularity which is typically associated with the Big Bang. 

Source: Wikipidia

The universe is expanding and just like a balloon the universe expands. The universe expands and keeps inside time and space contained in it like a balloon could contain confetti. The confetti is constrained by the walls of the balloon. The universe keeps all the laws and properties of the material world including time and space encapsulated.

The question is what is the balloon expanding on? Well if you are in a room, then the balloon is expanding in the room. Now, What is the universe expanding on? Well, the whole universe has to be expanding on a space outside the universe. For argument of reasoning, let us call this space or area Unknown Space of Expansion or USE. The material world laws and properties do not affect the USE. Timeless and Spaceless the USE view the universe from beginning to end. If God resides at the USE, then He is able to see 1 million years as 1 second or 1 day or 1 month or 1 year.

2 Peter 3:8

But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day.

Woodland Hill Church Audio: Already, but not yet by Greg Boyd