The key is to know how Stunt works. You start using it in the vegetative cycle because it triggers or elicits a flowering response in the plant, even before the light cycle has been switched.
The result is the plant producing more flower sites and growing bushier, instead of the energy going into vertical growth.
I'll give you the consultant's recommendation, but you can certainly use the recommended application amount on the label.
You use a set amount in the last week of Veg (.25 ml/L or 1 ml/4 litre (gal) and then 4-5 days before you change the light cycle, you give it 3 x that amount , which would be 3 x .25 ml /Litre one time only.
In weeks 1-3 of Flower you give it 1 ml to 1.5 ml per litre / 4 ml to 6 ml per 4 litres(gal) usually up to Week 3 but sometimes to Week 4 for a strain that tends to stretch or grow taller.