simon, please think about "GOD" as pure energy, light, as in rays, if you will.
in that condition, you being pure energy, pure for sure, there is no movement through time , (check your einstein) it is true.
So in that condition you would leave the past eternity (if it had a beginning) and travel to the limite of future eternity (if had an end)
IN AN INSTANT You would arrive at the moment you left.
so there is for "GOD" no measurable period PRECEDING the time when matter, dimensions lengths, breadths and widths started their journey out of the big bang singularity, with INFLATION et al happening on the way.
The big bang happened somewhere in the middle of eternity, and for somewhere of purity and energy, it would be always
THE NOW.
or thinking of our movement through time.
we live in the now, definitely not in the past (unless you are a history buff),
definitely not in the future (unless you are a jw, or believe in other unscientific fiction) so:
you are constantly on the MOVE in time. your NOW has zero length.
you depend for life of there being a future. Future time.
So There is TIME that is outside the moving universe, for the whole Universe is moving through time you and I with it.