Visualizer previews are limited to 15 seconds.
You can preview any 15 second segment of your song. Visualizers can be very resource intensive making longer previews too slow for comfortable editing.
You can preview a specific part of a song (a bridge, chorus, etc.) by moving the preview slider to the desired time, as shown in the video below. Feel free to create as many previews as you like.
As with other types of video, the maximum video resolution for visualizers is 540p, while the audio will be keep the maximum supported quality.