If I said anything that sounded Kantian to you, it was entirely accidental.
You cannot arbitrarily decalre God to be immune from the problem of existence simply by declaring Him outside of space and time.
There was nothing arbitrary in my statement. Any intellectual being existing solely within space/time (including physical laws, geometry, etc.) --- cannot be God for the very reason that Physicist gave in explaining why there is no "before" the big bang, i.e. no "south" of the South Pole. If the being only exists "in" space/time, the being cannot be "before" space/time.
The universe can also be seen as outside of space and time.
I am not aware of any Cosmology, Astronomy or Physics which allows this universe to exist except as space/time, e.g. the inflationary model. Space/time is created as the universe expands.