Does it affect them so they all move to the same X position? You have to remember that the events are run about 60 times a second, so if you only have a couple of Allens on the screen, it will appear like they’re all moving at the same time, when the reality is they got moved but with a few tenths of seconds delays.
That “wait” action won’t slow it down either - it just adds a delay to when the action kicks off.
You may want to look at this recent post that moves enemies randomly with the occasional pause. It may help with what you’re after.