First time posting here, I just installed OMV last week and I was having trouble with autoshutdown and I noticed booting up was taking a long time too. I saw some threads here that led me to realize it was the realtek driver but no there was solution so I wanted to share what I did to fix my problem. I finally have OMV working 100% to my liking and can kick Windows 10 to the curb.
My problem with autoshutdown was it kept waking up on its own after 180 seconds or it wouldn't properly go to sleep. First you need to see what driver you have installed. My mobo is old and there were no more bios updates. I knew it wasn't a bios problem because standby worked fine under windows. I have a Realtek 8111E nic, so from a terminal using lspci I could see it identified as RTL8111/RTL8168/RTL8169 and by typing lsmod i could see it was using the r8169 driver. This driver does not work right! You want the R8168 driver for best speeds and proper standby.
Kudos to realtek for addressing the problem and releasing a driver and script for easier install. Download GBE Ethernet LINUX driver r8168 for kernel up to 5.6, unzip the files and make the autorun.sh file executable by doing a chmod +x autorun.sh
Next you have to install a few dependencies while you still have internet access. If you login with root, you can drop the sudo. Update your system first too.
Make sure you do the following directly from a console and not ssh, you will lose connection as it changes drivers.
Change into the directory where you unzipped the files and run
sudo sh autorun.sh
This will uninstall the r8169 drivers and replace with r8168.
lsmod should now show the r8168 driver and I had no more problems with autoshutdown!
Thanks OMV team for such a great product, I hope this helps someone out there.