If the hairs are roughly 50% brown, you should be good to go. Check to make sure your trich's are at least milky, if they're clear, wait. I also want to make sure you understand that when we talk about trich color, we're using a microscope, not judging by eye. So be sure you keep this in mind. There are some strains that are purely a milky harvest. However, if your growing from bagseed and an unknown strain, do it right, don't listen to your friend (good call on that one) and keep checking your trichs, if they are milky, and starting to fall, harvest - This will give a good heady high, and the longer it cures, the more couchlock you'll get, but please keep in mind without pictures, there isn't much I can add.

Sativa is a long slender leaf, typically a little more like a tree when its not trained

Indica is a fat broad leaf, typically a shorter more bushlike plant

Something imbetween looks like your normal shots of basic weed aka MIDS

Post some pics