The first thing to look at are the stigmas (white hairs that are shriveling and turning red/brown). You want to see all, or almost all of those stigmas turn red/brown. Sometimes a bud will just keep growing at the tip, with some white stigmas, while the rest have turned, and it might be done. But that's not the case with the plants in these pictures. Only the tips of these stigmas have turned.
Once all the stigmas are red/brown, some people harvest. Others (like me) will take a magnifier and see if the trichomes have started to turn amber. They usually start to turn amber 1-3 weeks after they "look done" by the red/brown stigmas.
I would guess you have 3 weeks to go.