QUOTE(Blizzard)
How long does it take for a trigger action to take place?
Many trigger actions take place instantly and can be checked by the conditions of the very next trigger that is firing (such as setting switches). Other actions take more time to complete and may require a wait or short delay before testing against or modifying the results of the action. A typical example of a "slow" action would be moving or creating units. If you create or move a unit, you may wish to put a short pause (100 milliseconds or so) before checking if that unit is there with another trigger's conditions or modifying that unit with the action of some other trigger. Fast actions are setting switches, resources or score while slow actions are moving or placing of units.
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