The backup software should ideally be installed on the computer and not on a thumbdrive.
The limitation when backing up through a USB port to an external drive is usually how fast data can be transferred through the USB port.
The drive you are using to make the backup to is usually not that important as most will be able to accept and write the data much faster than the USB connection can give it to them.
The external drive that you are backing up to should be connected to you fastest USB port available. that's the 3.2 port in your case.
(Using the USB 2 port will still do the job but will take a lot longer to do it).
It does take time to make a full disc image backup to an external drive, there is a lot to be copied and transferred across, up to an hour is not unusual and it could be longer if you have a lot of data to backup or a large capacity drive.
Also remember that even if most of your drive is empty, say if you have a TB or multi-TB sized drive to backup, then the imaging software still has to scan every byte of that drive to see if there is something in it, it doesn't/can't just use the Windows file table because you may have other types of files on there that Windows doesn't know about, (say a Linux distro and files), so the imaging software has to check the entire disc.
As an example - this laptop that I'm typing on currently has a 500GB SSD as the OS drive, with about 88GB of that capacity used, and it takes Macrium Reflect about 50 mins to make a full image backup of it to a HDD via a USB 3.2 (gen 1) port.
(I'll be doing it later and will try to remember to add a screenshot here).