You are correct that from our stand point ‘time’ didn’t exist until Day 1 Genesis, however there is a continuum that exists outside of this reality. Probably not measurable with our time standards.
Otherwise, everything would happen at one time.
He uses the word forever in Revelation to describe several future events.
As to “why”?
You can’t box God in. He will do what He will do. Possibilities are endless.
That is true. However, there are quite a few things we are not meant to know until we are with Him. Don't worry about it as His extra-terrestrial actions do not affect our salvation.
Wait until we are meant to know.