How long should a full scan of a RAID 1 WD Duo take?

I’ve just purchased an 8TB WD Duo and have formatted as RAID 1, HFS+J. Primary use is for Time Machine Backup of iMac. All OK for a couple of days but ran into some issue overnight and have started running diagnostics. The quick ones both say it’s OK, so am doing a full scan to check. Any idea how long this will take? It appears to be doing about 10% / hour which would mean around 10 hours. Does this sound in any way right?

Answer is about 8 hours if it’s of use to anyone. So roughly 1TB / Hour …