How "present" must they be? Is this one of those things where one's mileage might vary and I'm asking a stupid question?
My first trunk novel had no antagonist. Everyone was "the good guy" and everyone had a pov. They just had mutually exclusive good guy goals.
I'm curious, did your story have very much conflict in it? Truthfully I've always felt the antagonist / villain to be the most important character in my story. Even more so than the protagonist / hero.
In Star Wars, Darth Vader's screen time comes to about 8 minutes. (I was curious, so I timed it.) But who has the most impact? Yeah.