It's not the time, it's how it's used.
Once Kane gets whacked the Alien is always on the audience's mind. There's never a moment in the finished picture where people just sit about talking about irrelevant shit -- it's always "How do we kill it?" "How do we survive?" "Well f**k the dude was an android how about we just f**king leave now yeah?"
It's like with the original Jurassic Park. That movie is over two hours long and there are dinosaurs for exactly 15 minutes, but whenever people find that out they say "Bullshit, really? I thought it was a lot more." Why? Because it was used properly and the film was still conscious of the dinosaurs when they weren't on-screen.
With Godzilla, the movie is about two giant insects crossing America to make baby insects. As they finally meet and make sweet love, some giant lizard comes up and murders both of them. And that's it. For 80% of the movie, Godzilla's entire contribution to the plot amounts to "And meanwhile, Godzilla is in the water swimming/waiting." It doesn't feel like a G movie because he has zero influence on the plot until the very end.
Movie monsters need as much off-screen presence as they do on-screen presence. Which is something every Alien movie from A3 onwards, including Prometheus, has been f**king awful at.