The Preset Crossfade slider allows you to choose the default timing for switching from one preset to another. At 0 seconds, displayed as "Instant," the lights will change instantaneously from one preset to another. Extending the time allows for smoother transitions, over which time the bulbs will seamlessly fade through colors from the old preset to the new. The slider allows you to choose times in 0.25 second intervals.
The Settings menu displays a range from 0 seconds to 5 seconds, but to extend the time even more, simply click on the blue "5 secs" in the upper right corner above the slider. Here you can set a custom duration of anything up to 59 minutes and 59.95 seconds, precise to the nearest 5/100ths of a second.