The last few weeks is when a lot of the weight gets b packed on.IME the buds start to swell around week 4-5, then a bit more stretch,then more swelling the last few weeks.
Get a 60x-100x scope to check maturity of the trichomes.
Clear trichomes = immature trichomes
Cloudy/milky trichomes = Mature trichomes
Amber trichomes = degdading thc
I like to harvest when thrichomes are 100% Cloudy/milky or 90% cloudy/miljy 10% amber.
Another thing to look for (in relation to trichomes and maturity) is to look for swelling of the calyxes and for the hairs to turn from white to pale orange and finally a reddish orange color aswell as the hairs receeding back in to the calyx.
Also,when you think it's ready....wait another week.
Breeders flowefing times can be subjective,if growing a hybrid you'll have to pheno hunt,plants in the indica range will finish before the sativa pheno but not necessarily....it's all depedant on growers skill,and environment.