Why doesn't iMac recognize Time Machine via USB cable?

[iMore Question]

I can get Time Machine backup recovery going via Wifi - but it will take over 300 hours to complete!! I'm trying to do it by connecting the Time Machine to my iMac via USB cable, but the iMac is not finding the TM that way!

 

[Bigeric23]

Is the drive with TM showing in Finder?