Bloom lasts 7-9 weeks for an average indoor strain.
Use from week 3-6 for a short strain, and from late3/early4 - 8 for a long strain.
As soon as you see that bud mass getting fat, start dosing bloom boosters- CAREFULLY.
When you see your trichomes mostly cloudy, stop using them and change out your res to pure water with just a touch of carb booster, a minimal level of calmag if you are running it, and at correct pH of course.

Time your ferts based on what your plants need for that life stage. Bloom boosters all have instructions printed on the back. I'd suggest reading them before use.