The stated number of days flowering is just an estimate, and are taken from plants grown in ideal conditions. Always figure on adding at least a week or two, sometimes more, to any estimated number from the breeder.
Most people harvest when the majority of the trichromes are cloudy/milky. For personal use, i harvest my indicas a bit early because I prefer more of an UP effect, instead of being couch locked.

Looking good for your first grow btw!