Cycle

This may be the equivalent of a year for Orcs; as young orcs do not get named until the Naming Day of the cycle they were born in.

Azeroth's moons
As Thrall is about to attack an internment camp, one of his men informs him that both moons are full and that maybe they should attack when it is darker. Thrall states that they cannot wait two more weeks to attack. It would seem that two weeks elapse between a full moon and a new moon.