According to the Constitution when is a presidential election required to take place?

The U. S. Constitution requires an election every two years.

In every even-numbered year, every federal congressional district in the U. S. elects a Representative to the U. S. House for a two-year term, and two thirds of the states elect one third of the U. S. Senators for six-year terms.

In every second federal election (in every year that is evenly divisible by four), the voters of each state also choose the electors who will elect the president and vice president for four-year terms.