One can't think of eternity as we think of linear time, another creation, in this world, which has a beginning and an end. Eternity has no beginning and no end, therefore, points on an eternal 'timeline' are meaningless, as is the imagining of an infinite timeline where no time exists.When
and where was God when he created HEaven?
One has to realize that thinking of Heaven as a location or world that 'contains' God, is also fleshly thinking and vanity. The Heaven of Heavens cannot contain Him, and it has not entered into the mind of man, neither indeed can it, Heaven and the glories thereof.
'Where and when was God when he created Heaven' is a foolish question. If you concede that God has no beginning, one could ask when and where was God 'before' He created angels? What was God doing in the eternity past prior to that (speaking like a man) 'moment'?