Targets of Opportunity can be inserted into the APF queue. Programs that are approved for ToO's can request a ToO. The total amount of time cannot exceed 2 hours per night.
In general, notification should be done with as much notice as possible. Right now, the only way to effect a notice is via email, but that should include requests for calibrations. There is a full policy document.
To request a target, send an email to the APF observatory scientist. Multiple requests will be served in a first come, first served order. Multiple requests for the same target will go the first receieved request.