I looked on the Canna site as I'm not familiar with their line. It does say add 3 weeks before harvest, so if you are going to finish right on 77 days/ 11 weeks yes, week 8 is a good time for it. However, 77 is the breeder stated minimum time and my last Triks run did finish right at 77 but I think a few more days would have been fine as well. Count on 85 days.
User Instructions
- Shake bottle well before use
- Add CANNA PK 13/14 three weeks before harvesting to a full nutrition tank in the following proportion: dissolve 15 ml concentrate per 10 litre of water (1:666). Add this mixture to the nutrient for 3-6 days
Since it will be going in over a few days I would maybe start it a couple days into week 8? Overlap into week 9 a bit in case your plant wants to run long. Good luck with it!