The feeding schedule is for plants in general not just weed and its a recommendation not law, its up to you to find out what your plant is lacking and correct it. Even in weed there are strains that flower from 7-15 weeks so just imagine feeding a plant nothing but bloom nutes for 4 months
Fox farm is good, you definitely need tiger bloom and a calmag additive, the big bloom is not really necessary from my personal xp.
Flushing is a bad idea, if your plant is yellowing from top to bottom (new growth) then it could be mag or the lights too close - if its from bottom up then its N thats deficient.
Ph issues can also cause symptoms