The Nicene Creed conveys an eternal begetting - the only begotten Son.
This begetting is not a matter of time, it is a matter of eternity. (Which is not 'a long period of time' it is another state altogether - an eternal state.)
'In the beginning was the Word' conveys that when the beginning began, the Person who incorporates, within himself, the concept of 'Word' (the sum of all that can be intelligently communicated) already was, in existence.
The Son is not 'made'. He is begotten.
And he is the only begotten Son of God.
There is a plurality - 'sons of God' - in regard to creation and these we see in Job. They are created beings.
There is also a plurality - 'sons of God' - in regard to redemption, by new birth, in a New Testament and in a New Creation.
But none of the 'sons of God' - by creation or by redemption - is ever referred to as 'the son of God'.
When the singular is used, with an article, it is clear that there is a personal singularity which refers only to one person - the Son of God, Jesus Christ.
His existence did not begin with the beginning. In the beginning was the Word.
The extensive writings of, for example, Athanasius, at the time of the Council of Nicea, clearly indicate the concept of eternal begetting. And also the concept of duality of nature : that Jesus Christ joins in his Person all the attributes of Divine nature and all the attributes of human nature.
These two natures do not converge or mingle or merge : they are two distinct things. They meet in the Person of Jesus Christ.