True Omnipotence is boundless. Whether there is one being or many, all would manifest the same Omnipotence, and the same boundlessness.
The distinction about "how long" a being has been Omnipotent would mean what is being discussed is not true limitless Omnipotence since there was a time before the being was Omnipotent.
With that sole distinction, a being who is and always has been and will be Omnipotent is "more powerful" than a being that ascends to the same rank of Omnipotence as the originator, But only due to the semiotics of Omnipotence.
From the point of view of a finite being observing all this, within their reference frame, if both Omnipotent beings pre-existed them and will exist after they die there is no difference from the perspective of that observer.