If the trichome bulbs have nearly all gone white and stubbornly resist turning brown/THC oxidizing, it can be harvested. If the % of white trichomes is higher than if some were allowed to turn brown (oxidize THC to CBN), theoretically the buds should contain higher % THC.
Sativas and larger plants can often go longer than 100 days. I'm happy if I (as usual) get ≥1 gram of prime buds/growing day, such as >100 grams at 100 days.