How long have they been flowering?
Buy a $10 jewelers loupe and look at the trichomes with it. If they're all clear it's too early, when they're turning milky you're starting to get close. When there are amber ones you are close.
The % of amber you will here all sorts of varying and argumentative answers from no amber trichs to all amber trichs. In my experience and from what I understand of the chemistry the more amber the trichs *generally speaking* the more of a couch lock type high you'll get (because of more THC-V)
The tl;dr answer, buy a cheap $10 jewelers loupe, there is no excuse not to and when all of the trichomes are milky and some % of them are amber, the more that are amber the more of a couch lock/body high you'll get (GENERALLY SPEAKING).
Also it won't hurt you to take a small bud off the plant, dry it and sample your plant now. Sure it won't be cured right etc. etc. but it will have the same % of cannibinoids as your final cure so you will have an idea if it's ripe enough or not for your desires.