That depends, do you want him silent on cue, or always? If you just want him silent on cue, then wait for him to solicit a click.
Your real goal seems to be for him to always be quiet, and for that you want to CR when he is not actively soliciting for a CR. And this should be really as random as you can make it to prevent drawing links to some undesired accidentally being linked as a cue. For example, if he is always getting a CR while he is preening and silent, he may think that is the behavior you are after.
Another point here is to be careful about not rewarding the screaming to the extent that you can. As social as aplomados are, he may scream just to get your attention. My current goshawk, for example, will scream when she wants to get put away from the weathering yard. And she starts screaming when she wants to go hunting.