Apparently at this stage of incubation the spheres were harmless.
"The Whispering Spheres" by Russell Robert Winterbotham
It is no longer in a stage of incubation.
"Masterpieces of Negro Eloquence" by Various
The stage of incubation is from three to five days.
"Special Report on Diseases of Cattle" by U.S. Department of Agriculture
In the early stages of incubation, at 100 deg.
"The Bacillus of Long Life" by Loudon Douglas
In 1956, three fertile eggs, from clutches that were at different stages of incubation, were immersed in water for 48 hours.
"Natural History of the Ornate Box Turtle, Terrapene ornata ornata Agassiz" by John M. Legler
During the first stages of incubation the germ is very distinct, even at the third day.
"Natural and Artificial Duck Culture" by James Rankin
The stage of incubation extends over a period variously estimated as from seven to fourteen days.
"A System of Practical Medicine by American Authors, Vol. I" by Various
Incubation may be shortened by retention of ova in the oviducts in early stages of embryonic development.
"Life History and Ecology of the Five-lined Skink, Eumeces fasciatus" by Henry S. Fitch
Possibly he may feed the female at earlier stages of incubation but I have not seen him do so.
"Life Histories of North American Wood Warblers Part One and Part Two" by Arthur Bent