There is a some dissagreement sometimes on how long a quench should be . Lots of my friends use a little longer , quenching is kind of personal depending on what kind of results you get with your method ,and the kind of steel you use . Myself using mainly 10 series of steel . In water I would go with 4 with oil 6 . too long a quench will sometimes not produce a good hamon. with w-2 a 6 sec water quench will turn blade very brittle sometimes. I think mostly its how you were taught . with 1095 in water it reaches full hardness in 3 sec . longer quenches usually result in more cracked blades from my experiance. I sometimes cryo treat my blades to reach a final desired hardness. After a cryo I always temp one more time , about 30 min. I get pretty fair results with this method. I also leave clay on until after temper , it seems to produce more activity that way . If you temper a differentially treated blades too many times ,you will sacrifice the hamon , which is basically a surface feature , depending on steel.