Thank you for your question.
That question of “when?” is a problem only when you are looking for a “beginning.”
The logical response is that there is no beginning for something which is eternal, for eternal conveys that “has always existed.”
Let us do a “logical” exercise. Let us say that we believe in “creation.”
Let us blame it on God as the actual “creator” of things. Then the question is: Who created God? 🙂
For some reason our devotional feelings (bhakti) have no issue on that simple question. We usually say, well God has always existed! If we want to be more “childish,” then we can say: “Is God separate from the space that He exists in? If He is separate then; who created that space where He is in?
If He is not separate then is God the space where He is in? 🙂 Logic can get us in “word trouble.”
Scientists came up with a “Big bang” for a beginning of everything. “It was a big explosion.” However, how the elements which “created” the explosion came into existence? Who created those elements? 🙂 Then, they will tell you that “You don’t need to ask this question, for everything started when time started and that is when the explosion happened…:-) BUt, we know that THAT IS NOT LOGICAL…:-)
Dear soul, forget about the world “creation” and your confusion will magically disappear. That word doesn’t exist but only in a dead dictionary surrounded by dead words. It is an illusion of the mind and illusion which is strengthened through our traditions and culture but an illusion nevertheless.
Existence has always existed.