It depends on the hard drive you have. A fast one (7,200rpm +), with a quick NTFS format should take about an hour, maybe just over, whilst a slower HDD (4,200rpm/5,400rpm) with a quick NTFS format should take about 1 hour 15 minutes. A 'non-quick' NTFS format would take you an extra 10 minutes, if i recall my experiences correctly.