When is it time to trim and dry?

Look at the trichomes under some magnification. Once you see all of them cloudy, half cloudy/half amber or just full amber you are good to go.

 

Your looking for 20% of the trichomes to turn amber .
Cloudy trichomes means the plants getting close

 

Full amber is a little late to be pulling.?
...Unless you want that kind of sedated high.

 

I personally will go for full amber. I like to get an indica feel with my sativas