This question is a bit difficult to answer considering civilizations generally don't go around recording the things their gods cannot do in great detail. However, strong assertions of both god's oneness, role as creator, and allusions toward his omnipotence mainly show up beginning with Deutero-Isaiah in around 500 BC. I've written a bit on this here.

That's not to say people sat around taking it to the logical extremes of "can he creat a rock so heavy he cannot lift it himself?" and pondering the implications of those straight from the start though, so it depends a bit on what you consider "omnipotence".

r/askbiblescholars might help as well.