ps checking the trichomes with a scope would be your best bet !
I just wanted to emphasize this point. Without a scope you're just guessing. Get something so you can check the trichs with.
Some seek good smokable Cannabis with uplifting highs. Some seek big fat buds that put the party to sleep. There are a hundred ways to wipe your ass.I personally feel this is a wives tale. A lot of people will advise to look at the trichs, but I read this thread on another site that is the absolutely best "when to harvest" thread I have ever seen.
The basic idea is like the great advice and pictures above from Maplemonk. The pistols should not be very visible. Ripe is when the pistols retract into and near the calyxes. The Calyxes will really swell up and the whole bud will swell. When you think you are done, go another 7-14 days. It will be well worth it.
I would say your plants are 4 weeks away like what Sour Deez said above. Good luck!