Set the entity in your map where you want it to spawn. Right-click the entity to bring up the editing properties. Set the entity to dynamic. (Static Mode: No) Set "Spawn At Start" to No and "Spawn After Delay" to Yes. You can set "Spawn Life" to some value to have the entity disappear after a certain number of seconds. Of course, you'll have to activate the spawning of the entity with a script attached to the entity or a trigger zone. The script also can be used to destroy the entity rather than using the "Spawn Life" value.
Life is about living.