We actually spoke some on this in our SS class a few months back. It was part of some studies we did I apologetics. Fortunately for us, we had a Ph.D. Physics guy in our class who works for NASA.
Here is my physics for dummies way of expressing what I understand.
First, time is really a measurement of distance. Without some sort of matter, there is no such thing as time. Think of it. What is a second? It is a calculated fraction of a minute, which is a fraction of an hour, which is a fraction of a day. Each of these were formerly measured by the relationship of some point on earth to some point on the Sun, and the rate of the change of distance between those points. Think of light years: simply a measurement of distance of how far light travels from A to B in the time it takes for the earth to cover a distance (the length of its orbit) of one full year around the sun. You cannot even conceive of time without matter.
Nowadays, our time is measured atomically. The cesium atom emits electrons at a certain rate. The length of the microwave from top to bottom is at a given measurement called a hertz. Cesium atoms consistently emit electrons at x number of hertz in what everyone agrees is one second. From there, essentially, our times are measured. Point is that time is a function of the existence of matter. No matter, no time.
It is also why you can't reach absolute nothingness in the physical universe. This is true of distance and temperature. Since all matter exists in space, and because all matter, even the indivisible electron, cannot be in the same space as any other matter, there is no true zero in distance. Time is FORCED into being by the very existence of matter because all matter requires distance. Without matter, there is no concept knowable as time. With matter, there is no concept knowable without it.
This is why some atheists can say "there never has been a time when there was nothing." It is true. But, saying that doesn't really mean anything since time requires a "thing". No thing equals no time.
Outside of time, God is. He is not a thing. He is the I am. He simply is and that is who He reveals Himself to us to be. He hung everything on nothing, according to the imagery in Scripture. Whereas there was nothing, God spoke and there was something. By His word, all that is came to be.
Atheists will argue that nothingness is illusory and matter has always been, that it has no beginning or end. As Dawkins says, nothing is really something. He says so with a straight face. He isn't alone. Of course, that merely replaces one form of belief with another form of belief, doesn't it? Saying everything always has been, and that time never wasn't, begs the question of how that is true. They say that nothing never was and matter always was, but can only speculate. We say that matter wasn't eternal, but that God is and He made something which is, in truth, everything.
It is indeed hard to conceive. I don't really. I don't know anyone who truly can except our Lord.