I too would say a week or two at the very most. Wait until 90% of the pistils have browned off. This will give you a true indication as to the biological health of your plant. Judging alone by trichome colour can be deceptive, some plants will never have amber trichomes and others will have 50% amber trichomes half way through flowering. Harvesting now/soon will give you a more happy and clear high, waiting another 2+ weeks will give you a heavy sleepy stone, due to THC breaking down and with increased levels of CBD and CBN.
Depending on which type of effect you prefer, should guide your harvest timing.
Hope this helps,........ Organoman.