I have a lot of plant hormones/etc (brassinolide,GA3,6-Benzylaminopurine,etc, etc) and have been playing with them for 10+ years on and off. On some plants GA3 is great, it was awesome when I used to grow Salvia. For MJ its usually, not great. The cliff notes version is basically you end up with stretched plants prone to hermi.
You're going to do it anyways so here is advice from someone who had used this at least a dozen times:
4 times is way to much (1-2 tops).
Also foliar @ less than 100-200ppm. I'd recommend 75-100ppm
earlier in the growth cycle is better than later. You can actually ruin buds with it, they will strech and almost go back into a veg state, new mutated growth will come out of them, its weird. If you have ever seen that barneys farm plant called Dr. Grinspoon, that is what you can accomplish.
Dont use it on a strechy plant.
So far I'm leaning towards Its best used to "fix" an overly compact plant not really to make a decent plant better. For example I have a squatty dense indica that is prone to bud rot, I'm considering dosing it to strech it out a bit.
Feel free to learn this the hard way.
If you want to "see it work" Foliar 200ppm 4 times once a week starting the first few weeks of flower. Just dont expect to harvest anything from that plant. Also GA3 needs to be "fresh" so to speak as it degrades relatively quickly in solution. You can buy mega gro i think its called but use it relatively quickly. I got pretty good results with that stuff on salvia and tobacco. I get all my hormones in powder form and mix them. (some are easier than others, some are water soluble, some need alcohol, some Polysorbate)
IMO its a great thing on some plants, unfortunately I don't think MJ is one of them.