Prior to egg laying the female provides an adequate environment for the developing eggs (assuming she has an opportunity to thermoregulate). It is important to provide an environment in the nest box that will be supportive to the developing eggs, also. This means appropriate moisture and temperature. I am careful not to keep the egg-laying medium too wet, spraying at least daily to maintain slight uniform moisture. Keep the temperature in the nest box the same as the incubation temperature (about 28 C or 82 F).
A normal, healthy clutch of fertile eggs is usually laid over a period of several hours. Eggs that are laid over longer periods of time (sometimes over several days) are more likely to be infertile or non-viable. However, I have infrequently seen fertile, viable eggs laid over a period of several days.
Time from successful mating to oviposition ranges from 42 to 55 days. Gilas have been known to lay from 2-13 eggs, the number being somewhat proportional to the size of the female.
Infertile eggs may appear smaller and more yellow than fertile eggs and will not be as turgid (they may appear "deflated"). Some infertile eggs will look every bit as good as a fertile egg from the outside. However, on candling there is no sign of a blood ring and they look more opaque on the inside (fertile eggs appear translucent when candled).
There are several possible explanations for infertile eggs. One possibility is the female was not inseminated at the optimal time. Another explanation is a problem with the viability of the male’s sperm. Perhaps he did not have access to appropriate temperatures earlier in the season and his sperm were unable to develop properly.