Formatting

if you used quick format it takes only few seconds to complete or if you selected it may take 10 -15 mins may be for 320 gb,(i never done full format with hdd unless there's some bad sector issues )

for 12 hrs it's too long , some thing wrong with your external HDD..

12 hours is right.

2 hours is normal for internal use. As you lose most of your speeds when connecting to USB, 12 hours seems about right. You can post a HDTune benchmark to see if there are any performance issues with your drive.

Any reason you're doing a long format? Doesn't make much sense on a HDD.