Rsync, hanging, OS 6,

The folder timestamps don't really make a difference.  Rsync uses the file size and "modified" timestamp to determine if there is a newer file.

I don't think you realize that most of the OS, including rsync, is just Linux, not something Netgear invented, though they have chosen the default options for rsync and given us very little control.  From what I can tell those options are  -v -8 --timeout=1800 --recursive --links --times --omit-dir-times --devices --specials --one-file-system --modify-window=1 --delete --owner --group --acls --exclude [name of any excluded file here] for an incremental backup with files deleted on target that are deleted on source and one or more files excluded.  From your observation, --omit-dir-times must be specified in OS6.x and not OS4.x (why, I have no idea).  I never noticed how it behaved regarding directory timestamps when I was still using an OS 4.x device.

If you have SSH enabled, you can use top  to see if rsync really is still running and what percentage of CPU it is taking.  You may need to add a filter by pressing O, then typing COMMAND=rsync to only show the rsync process(es).  If it's using a small amount of CPU time, it's probably going through files it does not need to update.  If it's a large percentage, it's probably copying a file.  If it's not really running, then something's amiss and you should stop it in Frontview.  I do see the CPU time sit at zero for a while when it's running, even when very little else is taking any time, so you have to watch it a while to see that it really is running.  I don't quite understand why, but surely it is one of the things that makes an rsync backup take so long.

I would love to have more control over rsync.  An RSync Plus app would be one way if they don't want all of the options confusing those who would never use them.