When is the 3rd generative period ?

No way you have 30 days remaining by looks of plant.

Right here soon I’d say.. cannas damn charts were always confusing. My buddy ran them for awhile and ended up accidentally going 2 weeks past ripe cuz of how they wore their stuff. That seems to be basically the point where you put on weight.. which you should be doing for the next couple weeks based on pics

The beautiful thing about nature is sometimes that it doesn't stick to any plans. From the pictures you seem to be still in Priode II. Since you are logging your values, you should be able to see when your plant needs more fertilizer and thus enter the next period.