How long does it take to lay an egg?

Two pair of Wood Ducks on a Southern Live Oak limb, second week of February, 2021. 

There were more than four, though.

The day after I took these two photographs, this happened.

The pair paddle up between 7:15 and 7:45 AM. The female leads, he follows. She jumps out of the pond, he jumps. Now, where is that box?

The female flies from a distance into the nesting box opening.

The male waits below the box. She is likely pruning down feathers from her body to add to the pine shavings already in the box, and she is laying an egg. 

(Thank you, Steve Rymph - he made and maintains this nesting box.)

Five minutes later, the female's head appears in the opening. 

She flies directly from the nesting box into the pond. He follows.

Then they do this ritual: He swims quickly ahead and turns around and swims toward her, both swimming in a prone posture. It must be Valentines week. (A blurry photo but you get the idea.)

She takes the lead paddling off with him behind her.

I've seen this three mornings in a row, but they might have begun days before my sightings. 

Information from Birds of the World: 

She lays one egg a day until the clutch is complete. Sometimes she skips a day. 

A clutch consists of 6 - 16 white-colored eggs.

Only females incubate.

Incubation starts 3 - 4 days before clutches are complete.

She incubates for about 27 days.

I hope I am able to photograph when the ducklings leave the nest, which happens within 24 hours of hatching.