Yes region 48 will take a long time to backup, probably not overnight though. It will be the full size of the available space for the visible files system, i.e. if your unit has 1GB the 48_backup.bin will be 1GB also. You'll know when it's finished because it'll go back to the bootloop when it tries to execute the 'reboot' command or just freeze. When you get the full 48_backup.bin file open it in PowerISO or similar then you can take a copy to keep as a backup on your PC. If the problem is really that there's something in the visible flash stopping it from booting rather than a hardware problem, writing back 48.bin with just an empty Garmin folder in it might be enough to boot it.