I tried and it seems that you can only pause and continue within the same session. I tried the "continue later" button (you have to set the setting to allow multiple instances). I set the time for a few minutes later and when that time came, it started a new session and seemed to start the whole process over. I didn't reboot, but I if it doesn't resume without rebooting, it likely wont after rebooting. So bottom line, it doesn't appear you can do that. Perhaps there is some other setting that needs to be set but I didn't see any.
Actually I tried this with Blu-ray Copy, but I assume it would work the same with UHD Ripper.