I've used cannazym throughout the entire grow (well starting at 2 weeks in when they were .. 'healthy' veg stage plants .. no point in adding something that kills dead roots in a 1 week old seedling with .. no dead roots yet. I also don't use it in the last week of harvest when I just give straight RO) and had excellent success.
I am using the whole canna lineup (that is, their coco substrate/medium, A+B, rhizotonic, cannazym, PK13/14 ... and .. NOT cannaboost, not paying $130 for a bottle of anything
), so I don't know how my experience would apply to cannazyms use in other mediums/nutrients.
However, given that cannazym is simply a medium (coco in my case) conditioner, has no dissolved salts (so its addition to your tank won't change EC much/if at all) and my own personal success I would definitely recommend giving it a try.
It's also excellent for reconditioning a soil-less medium if your the type of person who likes to reuse their coco for some reason.
There are several companies that make the same product (well similar, their own formulation), such as Sensizym, but since thats made by AN, I will never use it
(besides, I have been very pleased with the quality of all the Canna products i've used, as well as the bounties they've produced for me
)