When it is the only possibility that remains.
How do you know it's a possibility? We can't solve one mystery with another mystery Old Navy. And we can't explain one unknown by postulating the existence of another unknown.
This would be like saying, "Well I couldn't find my key's this morning therefore bigfoot took them - it's the only remaining possibility."
Absent some evidence that bigfoot exists and is the sort of creature that takes keys - then it is not valid to say it's a possibility. In order to say something's 'possible' we need either precedent or something of parallel comparison.
The same is true with universe creating gods. Until such a time as it is demonstrated that gods do in fact exist and they create universes - then it's not valid to assert that it's "possible".
I'll also point out your attempt to equate creation to evolution is quite silly. While there is no evidence for gods there is massive amounts of evidence for evolution - which is demonstrable with measurable accuracy.