A monster is considered to be on a Timed Spawn when its appearance in the game is restricted to certain times, or the creature is limited to appearing a certain time after it was previously defeated. Timed Spawn monsters are unlike Lottery Spawn monsters as they are independent of any other monster spawns in the area.
Strictly speaking, most monsters in Vana'diel could be considered to be Timed Spawn monsters, but this term is most commonly used when referring to Notorious Monsters with long respawn times or monsters that spawn only during certain hours of the day.
Some Timed Spawn monsters have slightly randomized spawn times, with one or more spawn windows in which they can spawn. However, this behavior is only present in a small percentage of Timed Spawn monsters; most monsters can be precisely timed between spawns.