How does length of daylight vary from season to season?

The earth has seasons because the earth revolves around the sun

The ITCZ varies according to the seasons due to the same factors that cause the seasons themselves... the earth tilts during the year and that is what causes the seasons. The ITCZ over land tends to...

Earth's axis is tilted 23.44°. This has the effect of making the sun low on the horizon during winter, and higher during the summer.

In the summer, as an example, the sun is up for more ample of a time, thus a longer day. In the winter, the sun is up for a shorter time, which counters with a shorter day.

In the summer you have more hours in daylight.