daytimeForecast and overnightForecast Availability

When pulling via the REST API DayWeatherConditions objects from the forecastDaily data set, I'm noticing that for today's DayWeatherConditions no daytimeForecast nor overnightForecast is available at 8 AM each day in my location, but will be available a few minutes later (say 8:05 AM). What explains this inconsistency?

In other words each day day at 8 AM I pull and the returned dictionary is missing the optional key/value pairs for daytimeForecast and overnightForecast, but a few minutes later after performing the same exact request, they are available.