Here's why:

* The tropics are located between the Tropic of Cancer and the Tropic of Capricorn. This region experiences relatively consistent day lengths throughout the year.

* The Earth's tilt is the primary reason for varying day lengths. The tropics are close to the equator, which means they receive roughly equal amounts of sunlight year-round.

* Slight variations may occur due to the Earth's elliptical orbit and other factors, but the difference from 12 hours is minimal.

So, while there might be subtle variations, the day length in the tropics in May is generally considered to be around 12 hours.