you can start using the pk13/14 even earlier then they recommend as long as your not burning your plants i would introduce it now dont even wait a week use it,right now im running all of the Canna nutes Coco A & B,Rhizotonic,Cannazymn,PK 13/14,CannaBoost(witch is wicked for foilar even in budding phase) do you use a PPM meter or PH pen?? If so you can determine if you are feeding them too much nutes or not enough,i use the Canna schedule just as a guideline but dont follow it to the T because every strain is diff and some like more or less nutes at diff times just gotta get to know your strain well...PM if u got any other questions as i probably wont come back to this thread!
Goodluck with the ladies!!!