Time is merely the product of our minds. Imagine a group of children who had been raised in a hermetically isolated situation without any language for time. They found a huge pendulum hung in their house, and every morning they started it swinging. They had been taught to count, so each swing they chanted "one swing" then "two swings," etc. They were soon able to say "dinner is at 250 swings." The word time would not enter their language, and time had no reality apart from their habit of counting pendulum swings.
What about the dimension of time? Dimensions are merely directions of movement which can be measured . We can measure laterally and vertically to yield the three dimension of space. Then we add sundials, the counting of pendulum swings, nights and days, phases of the moon and the annual movements of the sun.
As we translate every use of the word time into measurements on a sundial, counting swings of the pendulum, rotations of the earth, phases of the moon, etc. it soon becomes obvious that time has no reality apart from the construction of our minds. So when we say God is outside time it can only mean that God does not count and measure in those ways.
Nor does it make sense to talk about time going backwards. You cannot
make a pendulum or the succession of days and nights go backwards. The
slowing of time is merely a function of the length of the pendulum or the
observed rotation of the earth. The slow reduction in the ages of the patriarchs
in Genesis for example could by the equivalent of a change in the orbit
of the earth Whether or not that is a possibility, God is neither in or
out of time since we merely invented it as useful tool of our language.
There are many experiences that cannot be quantified (beauty, joy, love), and physics cannot deal with unquantifiable experiences. It can only deal with what physics calls dimensions. Geometry began when humans discovered it was possible to measure width and length and height for pyramid building, etc. and so those experiences became dimensions. Then by use of the sun dial and pendulum the dimension of time was developed. Weight had always been experienced, but it became a dimension when balances and fixed weights allowed measurement.
My point was that God is not limited by the need to quantify. That means
He is not limited by our quantified dimensions. But He does have an experience,
frequently described in the Bible, of the past, the present and the future.