Why is Indesign Exports so Slow? 8 cores and it only uses 10% of the CPU

The response is very simple.

PDF export from InDesign is single threaded although the writing to disk is buffered.

The nature of the PDF export operation is such that it is very difficult to arbitrarily assign multiple asynchronous processes to it. Optimizing embedding of fonts and detecting reuse of embedded images are operations that pretty much require linear processing of the InDesign document. And if your magazine has many, large, high resolution raster images, compression and downsampling of those images are fairly CPU-intensive.

Quite frankly nine to ten minutes to export a high quality PDF file from a very graphically-rich InDesign document with many pages doesn't seem all that bad. 

One thing you might check are the settings you use for PDF export. Adobe recommends PDF/X-4 without any color conversions. PDF/X-4 files have live transparency. Transparency flattening is exceptionally time and resource consuming. That may be a factor in what you are experiencing. (Note that preflattened content with conversions to CMYK are old, deprecated workflows that generally lead to lower printed as well as display quality!)

                - Dov

As you mention InDesign Server, here's an idea. Break up the file into 4 separate files (a script can do this), then fire up 4 instances of InDesign Server (with a Server license you may run as many instances as needed, I believe). Use each instance to export a different section of the magazine, and when it's done combine all sections into a single PDF in Acrobat.

This should cut the export time down to 25%. But chopping up the InDesign files can be slow (and destroy cross-references). So probably not a solution....

Are you exporting as a background task (async exporting) or have you disabled that option? (https://geofffranklin.com/disable-adobe-indesign-background-tasks)

I don't think this makes a difference to speed, but with the old export you get 2 progress bars so you have more information as to what is happening, and you'll be able to tell what is slowing things down, perhaps.

It may also depend on transparency flattner presets you're using, as well as whether artwork has to downsampled during export (in which case, consider doing this separately in PS so that all artwork is at the correct resolution in InDesign).

An hour to export a document seems too long. I haven't worked much on fully-fledged magazines with tons of transparency, etc., but I regularly export 300+ pp books full of pictures and illustrations, and rarely does an export take more than 2 or 3 minutes. 

RAM and CPU resources are allocated automatically. There are other factors at play when exporting, like linked art (how big) and the location of these files (slow server?). Try turning off preflight, if it's on. Or you can try to make Indesign not export it in the background, although i don't anticipate any huge diffeerence. 5-10 minutes might seem long, but one of my pdf took 45m yesterday (10GB of linked art on the server, used in 7 OOH banners). This is on a iMac Pro.