Well, for 142 games it's definitely going to take longer than 30 seconds. Let me make sure I understand this correctly.
You have an external usb drive X, which is formatted to FAT32 and contains 142 games. You want to move them to usb drive Y which is formatted to FAT32. They're both plugged into your Windows computer at the same time, and you're trying to copy from one to the other with no intermediate steps, correct?
I assumed the drives were FAT32, but since you mentioned Wii Manager, I have to ask. Are they FAT32 or WBFS?
With FAT32 drives, you best option would be to copy everything from drive X to your computers hard drive, and then copy them from your computer to drive Y. I did this and it worked flawlessly. I'm not sure if that would be an option with WBFS drives. The problem with usb drive to usb drive copies like that is the main bottleneck is the USB 2.0 interface. Since you're pushing all those bits of data up and down that pipe at the same time, you're effectively cutting your throughput in half (actually it'd be less than half, due to overhead processing and whatnot). Plus, if you ARE using a WBFS drives, you're computer is going to be doing a LOT of processing to make that happen, since it would have to convert those files to NTFS and then back to WBFS (I'm assuming, not 100% sure on that).
You can always look into utilities such as EaseUS Disk Copy (Free Hard Disk Copy/Clone Software for PC & Server Hard Drive. Disk clone, disk backup, disk image and partition copy freeware.), although, I'm not sure if that would work for WBFS filesystems. Being that it can do a sector-by-sector copy, it should be able to.
At any rate, the ETA for file transfers is largely speculative. The computer will likely report elevated numbers while it's indexing the drive and preparing to copy. I bet, once the files actually begin transferring that time would drop significantly.Personally, I would give it a go and let it chug away all night; it should be done by morning. I remember doing that with modem transfers at 14.4K using the ZModem protocol... now those were the days.
There. Clear as mud? ;-)