In many cases, the female begins to incubate her eggs as soon as the first one is laid. Usually the eggs are laid in the morning, about 48 hours apart. However, this can vary from 24 to 72 hours. The eggs hatch in approximately the same time sequence as they were laid. If they do happen to hatch at the same time, this means that incubation did not start until the second egg was laid.
The female, who incubates the eggs alone, leaves the nest frequently during the day to feed and/or gather new reinforcing materials for her nest. The time each species sits on the eggs in the daytime ranges from less than a minute to three hours per sitting. Absences last from less than a minute up to half an hour. The number of times the nest is left varies from 10 to 110 per day. Even with the most frequent absences, the hummer's eggs are kept covered from 60% to 80% of the daylight hours. These foraging trips may contribute to the relatively long incubation period for such small eggs. In general, the minimal incubation period is from 14 to 17 days, but may be prolonged by inclement weather or harsh nesting conditions. — Nesting Behavior of Hummingbirds