When the pistols curl in and the third set of pistols are the last to curl in (about 80 percent of them) and the plant doesn't drink anymore. these pics look like they are early, but Im a noob,
Another way to tell is by looking at the trichomes through a jeweler loop, if you see some amber, they should be ready, too much amber it'll make you sleepy.
Time in the pot is just a guildeline. My soil, temp, humidity, light is not optimal to gauge by days, in otherwords, all set ups are different, so time to harvest would be too.
Hope this helps and more than hurts.