Are you using a 60x jewelers loupe/microscope? At least 30x is needed, but you probably need another week or two. A good rule of thumb is about 10% amber. Don't look at preflowers either, as they are older than the rest of the plant, they won't be accurate. At about 10-20% amber, it's safe to assume in my opinion, that you can chop. It can be very difficult sometimes with 15 micron trichomes to see anything but amber and not Amber. Also do not check sugar leaves, but calyxes only. Top colas usually finish a few days before the rest of the plant, but a healthy plant that has been defoliated at the right time should finish all around the same time.
Some hybrids/sativas finish long after 56 days. Most indica varieties finish between 8-9 weeks. Rarely 7 in my opinion (although you could, but not ideal.)
