If you forget the whole idea of an 8 week flowering time you'll be much better off,you'll have a stronger more powerfull smoke with much heavier yeilds when harvest is dictated by watching new pistil growth along with trichome maturity,then deciding when to chop,calender days are meaningless.
How long was veg & how large are the plants going to be before going 12/12,these 2 issues along with durration of budding have much more influence on yeild over what type ferilizer or what type soil.
A fairly experienced soil grower should easily pull a heavy ounce per plant with one month veg time,if your grow goes well with no major issues your looking at around 3lbs or so depending on conditions & prior experience,fox farm products will contribute the least of all pertaining to yeilds.