When to swap Vitalink buddy to Vitalink PK then back again

The switch should be the week(s) flowering have a peak. Seeing how your plant look like actually i would say use PK week 10 and 11 and switch back to buddy for the few last flowering week(s). Your plant will prolly need more than 8 week of flowering that the vitalink schedule show, decal feeding accordingly as your plant will prolly need more something like 10 -11 weeks of flowering i would say. Happy growing.