Final answer:
The number of daylight hours is always greater than or equal to nighttime hours from the vernal equinox to the summer solstice in the northern hemisphere, beginning around March 21 and culminating around June 21.
Step-by-step explanation:
The time period during which the number of daylight hours is always greater than, or equal to, the number of nighttime hours for observers in the northern hemisphere is from the vernal equinox to the summer solstice. This period runs from about March 21, when the day and night are approximately equal in length, up to about June 21, which marks the longest day of the year with the shortest night. This is due to the tilt of Earth's axis, causing the Sun's path across the sky to lengthen as we move from the vernal equinox to the summer solstice.
After the vernal equinox, the days begin to get longer as the sunrise and sunset points migrate northward. This culminates at the summer solstice, when observers experience the most extended period of daylight in the year.