This page explains what happens between arming a cue and firing it. Nothing here needs setting; it explains a behaviour you will notice, and one you might otherwise mistake for a fault.
What the program does
The armed cue is prepared in advance. A web page has to load, a scene has to be built, a media file has to be opened and moved to its in point. From the moment a cue turns green, the program does that and holds the cue ready. When you press GO, the picture is there immediately.
The list arms the next cue by itself after every GO, so by the time you reach for the button, the next one has been ready for a while.
What you can see of it
Not much. A web page cue that was armed a few seconds ago comes up instantly, while one you arm and fire in the same second may still be assembling itself.
What is not prepared
A media cue is not played in preview, so a clip cannot reach the output by accident. Video and audio only run when they are live — never while merely selected or armed. An armed cue shows in the next-cue picture beside the preview — a clip paused on its first frame — while the preview and the output keep showing what is on air until GO.
A countdown in a scene stays frozen until the cue goes live, so the clock starts at the moment the audience sees it rather than at the moment you armed it.
Practical advice
Give the program the moment it wants. Arm the next cue as soon as the current one is running, rather than at the second you need it. On a list built the ordinary way — where the following cue arms itself — this happens without you thinking about it at all.