As the word itself says, they are autoflowering, they start to bloom automatically regardless of the photoperiod (amount of light hours) they are exposed to.
There are many growers who think that 18/6 is perfect for our plants and others who believe that 20/4 works better because it increases production.
Personally, I do 18/6 the first week and then 20/4.
And good luck with the grow!