Answer:
The number of daylight hours
Explanation:
The number of daylight hours is not a factor in the regulation of Earth's seasons, it is actually a consequence of seasons and its regulation factors.
Summer, for example, is the season when there are more daylight days and it is a consequence of beeing nearer to the sun what depends on Earth's position respect to the sun, its axis tilt angle.
Earth's orbit is elliptical and it makes that sometimes Earth is very near to sun and sometimes it is far from sun; besides, Earth's axis has an tilt and it has a sequential variation, this variations make north hemisphere to be nearer to the sun for a season and then it will be far from the sun while south hemisphere is nearer, being in its summer season. Finally, seasons temperature depends on the amount of solar energy received at the surface, which at the the same time depends on the angle at which the sun strikes the surface, what is regulated by elliptical shape at Earth's orbit and the angle of Earth's axis tilt.