Interval
Interval is a mechanical term involved in Rituals.
An Interval denotes the Action speed at which you can perform Checks to progress a Ritual.
Example: If Johnny Tutorial was attempting to perform the Setup - 80 Ritual on his favourite Heavy Sniper Rifle, that Ritual has an Interval of Action. Johnny could only perform a Skill Check any time he could perform an Action, each one costing him an AP.