the sites I looked at report lethal purple as an early flowering 80% indica variety that grows fairly large outside (at least for an indica dom plant). They also report a strong parfume smell which may help you judge when it is ready...do you have any way to look at the trics? that's how I would figure it out, pistle color would be my second choice...and if all else fails I would just take it about 8 weeks after flowering began (July 20th?) though they look more like 5 weeks away rather than 4 to me from the pics...I am sure you will be able to havest within the window just using your experience and judgement. Best of Luck J-Angel