I have an approximately 2 year old Pekin/Rouen female. We have always pulled her eggs. This year, we decided to let her try to hatch some ducklings. This is new for all of us so we are learning together! 
We have just her and one male. Her nest is beautiful in a nesting box in their enclosure with now 12 eggs. I never see her sitting. She just lays and goes about her day, frolicking in the pond and eating.
How do I know when to call it? How long can her eggs be in a nest with no incubation?

We have just her and one male. Her nest is beautiful in a nesting box in their enclosure with now 12 eggs. I never see her sitting. She just lays and goes about her day, frolicking in the pond and eating.
How do I know when to call it? How long can her eggs be in a nest with no incubation?