Need more info. Stuff like...how long have they been flowering, what strain, what size pots, which nutes and additives.

A picture would help, too.

Just going by your trichomes description...it shouldn't be long till they are ready...depending on the effects you wish to get from the smoke. Want a heavier, couch-lock effect...let 'em go a couple of weeks (perhaps a feeding or two inbetween, and a final flush (no more nutes) within 3-5 days of harvest)

If out of smoke, and prefer a more social (less debilitating) effect, would start to considder harvesting.

Not knowing what strain they are, or what condition they're in, or how far along they are...that's the best I can offer.