With the right year I can absolutely get oak below 20% in a year. But if it is especially humid or lots of precipitation it doesn't happen. 2 years is almost always good for me.Stacked out in the open where it can get plenty of wind and sun...and its top covered too (sides open)
6-8 months is only enough for a few species...most take a year plus...and a whole bunch more need 2 years...and a few, like Oak, need 3 to be really right...yeah, you can use it in 2, but it lights easier, burns cleaner, and makes more heat at 3 yrs CSS'd.
If you insist on burning <1 yr CSS Oak, then I vote we change your Hearth user name to "Smoldering"