As an example, I have 2 autos growing right now that are supposed to be the same strain; both receive the same light, water, etc. They are 11 weeks from seed and one is fat & sassy, looking like she might be finished in another 2 weeks, maybe. If it matters, the trichomes are starting to cloud, still a lot of clear with an odd random amber one here and there, but this isn't how I determine when they are done. The overall look of the plant will be the major indicator.
The other plant, on the other hand, is just starting to flower and if I had to guess I'd say she'll be done in another 6 - 8 weeks, maybe; really can't tell at this point.
By the way, tomatoes have trichomes and you don't harvest tomatoes based on the appearance of the trichomes. You harvest the plant when the fruit has fully ripened. Your bud is your fruit, harvest it when the bud looks ripe. Good luck next time.
And you know those tasteless red balls of water they sell at the grocery as tomatoes? Harvested too soon; just saying