No doubt this will be an easy question with an easy answer, Anyway..
HDD became unformatted and would only appear in windows as 'RAW'. I had to initiate it and perform a quick format so Recuva could do it's thing.
It's a 3TB HDD which was half filled. Recuva says it'll take 20 hours to finish it's scan, and it has 12 hours left. After it finds the missing files, am I able to copy them straight back onto that same HDD? Or does it have to be to another disk?
Physically, you could copy the recovered files to the same disk, but it will almost certainly overwrite what you are trying to recover, so the exercise will end in tears.
Sensibly, you should recover all files, no matter how few or many, to a separate drive/partition.