If you're unsure about whether it is ready... try estimating the brown hairs.
You want 70% red. You see that, then step back from the plant and ask "Are you ready?"
You never know, she might say yes. Also there's no harm in taking plants at different stages of readiness. Most strains have a window of ripeness. You can pick them at the start of the window, or hold your nerve till right till the end. As a new grower you're meant to take some early anyway. You need to get a feel for what is right. So in all, you really need to use your own instincts on this one.
If you're not sure, take a bit at a time and examine it in normal light.