The tichromes are what will look like white dust on your buds when they are near mature. It will likely be @ least 6 weeks from the time you cut lights to 12/12 b4 they will be close to ready, 8 weeks is pretty normal. So I don't know when you'll start seeing them well but I would say by 6 weeks of flowering you should be able to see them. Like i said from a distance it will look like white dust. But if you get close & look w/ a magnifying glass, a jewelers loop, or other magnifying device (I have a 30x geoscope that is more or less a kids toy) then what appears to be dust from a distance is actually the tichromes, which are little mushroom shaped things. A small stalk w/ a droplet of moisture (or resin maybe?) on the tip. So when they start, the will be clear on the ends, as they mature the ends will turn cloudy/milky, then when they go past their prime they will turn amber.
So ideally you want to harvest when you have the most cloudy ones. But they don't all turn cloudy @ the same time, so you could have 40% clear & 60% cloudy, or you could have 10% amber 85% cloudy & 5% clear (this would be a great time to harvest).
Anyhow what happens is if you harvest too early & too many clear tichs, then it won't be as potent as it should be. After the tichs turn amber (as I understand it, I hope my terms aren't off), well when they turn amber the THC is converting into cannabanoids, which means the buzz you get will be turning from a more desirable cerebral high into a very stony, immobilizing, put you to sleep kinda buzz. So harvest too late & you will have very sleepy weed, which already is the tendency of most indicas so you don't want that either.
So like i said, you wanna harvest w/ the most cloudy tichs, which I would say is usually around when you have 5-15% amber tichs.
I'll also see if i can find a good close-up pic of some tichromes so you can see & post it shortly.