Video export takes too long

An hour-long comp is an eternity. If your comp won't generate a ram preview at full resolution with all effects at the rate of 7 or 8 frames per second then you need to redesign the comp or figure other things out. Unless something drastically changes in the timeline, watching the Info Panel while rendering a preview will give you a pretty good idea of how long it is going to take to render your project. If the ram preview is really slow try turning off some of the effects or changing the design. Most of my comps are seven seconds or less because I work mostly on visual effects for movies. My design limit is about 1 or 2 minutes a frame for full ram previews. If the comp takes longer than that I simplify or pre-render segments. 

If I were tasked with creating a music visualizer that needed to be an hour-long After Effects is the last tool I would use. There are dozens of websites and other tools for that that work much faster. If you must do it in After Effects keep the frame rate to 24 or lower. 29.97 is the highest I would go. 12 fps was fast enough for Buggs Bunney, Yosemite Sam, and almost every other hand-drawn cartoon ever made and it's plenty for most music visualizers. 

If you are going to do more than one of these using After Effects then invest in a background rendering solution like RenderGarden. I have five different ones and RG is my favorite. On my 8 core machine, a render that would take about an hour using the Render Queue/Output module (faster than the Media Encoder for most projects) will take about 12 to 15 minutes and I end up with a lossless production master and an H.264 MP4 for client review at the same time. 

Turn off Video (i mean off only Eye icon in your video layer), just export the audio spectrum layer with Transparent BG.

now combine both in a new composition and export. hope this may work.