I believe this is consistant with obervations of Black Swifts at Black Canyon from 1996-2017, as reported in "Breeding Phenology and Success of Black Swifts in Box Canyon, Ouray, Colorado" in the Wilson Journal of Ornithology, Vol. 119, No. 4, pgs. 678-685, 2007 by Sue E. Hirshman, Carolyn Gunn and Richard G. Levad. Since publication of the original article, my understanding is that Sue Hirshman continues to closely monitor and record data on nesting swifts at Box Canyon, and Dr. Carolyn Gunn works with the data to update statistics (and continues to publish scientific papers about Black Swifts). The updated statistics were presented by Carolyn Gunn at the 2019 Ute Mountain Mesa Verde Birding Festival, and included the following:
Egg Laying - mean June 28 (range June 15 to July 22, n = 118)
Incubation Onset - mean July 1 (range June 16 to July 23, n = 131)
At her presentation, I recall Carolyn Gunn commenting that Black Swift eggs can remain unattended after laying for several days, and the eggs will not addle, and will remain viable.
As Rich Levad said - this is the coolest bird.