look at the trichs.

i usually havest at 50% cloudy/ 50% clear, with a few ambers in there.

you will need at least a 30x mircoscope or mag glass.

Don't go by the hairs. I would start checking alot by the end of week 7 and start of week 8 and keep on checking, just because it is mainly sativa, doesn't mean it wasn't bred with a indica somewhere in its genes, to have it flower faster.