At the beginning of the battle between Dutch and the Predator, we see a shot of the Predator jumping between trees. In this shot, we see the sky and there is still a lot of light indicating that it is still daytime. The actual fight however, takes place during the night.

More: at the end of the film, when Dutch fights and defeats the Predator, it is night time. However, when the camera switches to the view from the rescue helicopter, we see the Predator's explosion in broad daylight! AGAIN!