Is this normal behavior?

I observe daily, from a distance, the behavior of this female mallard. For weeks now she seems to leave the nest for long periods of time. I came today, she wasn't there. A male mallard came from the pond and seemed to peck at the eggs. He then left. The female returned, pecked around and then left. After 30 minutes she returned and sat on the nest. It was cold outside. She must have been gone for 45 minutes. Is this normal? Could her eggs have survived that long? Could the male have eaten an egg?