It means 8 weeks of just flowering until it is at it's peak ripeness and should be harvested. You can veg a plant as long as you like, (maybe not good more than a year).

BTW, you cannot harvest a plant by the calendar. 8 weeks is based on the breader's optimum conditions, meaning light, temp, etc... When the calyxs seem done swelling switch to water and then wait until the trichomes seem at their peak for your particular strain.