Lighting; Time of Day
Lighting is so important.
There is a good reason your photographer is strict on the start time of a session. Lighting is everything.
Be prepared for your session. Arrive on time, all photographers appreciate this! I help guests from out of town prepare for this as they don't always know what to expect in these mountains. Weather is a crazy, rolling through mountain summer storm or a recent snowstorm. It will be so, so worth it. Light is fleeting at sunset. Plan to arrive early, let the kids acclimate and get used to the area. I promise it will be worth it ;)