Inside the Preset Editor's "Color Controls" for any given Assignment, you have fine-grained control over the duration of each step in the animated color loop. Under "Animation Steps" you'll see a series of colors and arrows representing each step in the loop. When you tap one of the arrows between two of the steps, you'll see a "Step Duration" area where you can quickly change the length of that step.
Drag the slider to go up to five seconds (in quarter-second increments) or tap the number itself (in this example, "1 sec" in the screenshot) to bring up a panel giving you more options like values longer than 5 seconds, or finer-grained control.
Try experimenting with "Fade Between Steps" depending on whether you are going for a smooth animation or something more punctuated. Check out the Starter Pack of presets for some examples of how adding fade (or leaving it out) can produce some fun effects!
Finally, if you have the relative timings of all your steps just how you want them, but feel like you need to speed up or slow down the whole loop, use the controls for "Overall Duration". For example, if you have a loop that's one second of red and one second of blue, you'll have an overall duration of two seconds. If you were to drag that up to five seconds, you'll see your two steps scaled up automatically, to 2.5 seconds each.