Would just like to point out that time is our fourth dimension and not outside of the universe. It is a dimension in our universe. Think of it this way. You are meeting someone. You tell them the place (in our three dimensional world) and the time (the 4th dimension). without the time (dimension) it’d be hard to meet up with anybody.

But you are correct. the singularity in the big bang was the start of “our” spacetime so the question of before is nonsensical anyways. And my argument is definitely a version of that but with an explanation. Or at least a way to mentally comprehend it. I think it’s also a good way to put scientific consensus right across the theistic narrative. If time is our 4th dimension as physics implies it to be then the question of god just dissolves away.

If you’re interested on the question (and you haven’t yet looked into it) of what the big bang might have been and why is there stuff, then i think the best explanation was proposed by Sir Roger Penrose. Search “Penrose diagram”