I'm sorry but I have to disagree, the size of the buds has nothing to do with finish time. That is most likely due to genetics/lights/growing conditions. There are 3 main indicators that let you know when a plant is starting to mature (besides trichome color):
1. Tops begin to crown and stop growing leaves
2. Calyxes start to swell up and pistils shrivel and die
3. Trichomes grow stalks, like a "ball on a stick"
Your plant exhibits all 3 of the above. At this point the best way to tell is with a microscope. I would say 2-3 more weeks, but that is a rough estimate.