Many growers believe that the start of flowering is the day the light duration changes, i.e., the "flip". Others don't believe that's true, including me. Instead, they think the start of flowering as being when buds appear and that the time between the light change and the appearance of buds -- known as the "stretch" -- is the last part of the vegetation stage. So, accordingly, that 10-to-14-day period shouldn't be counted as flowering time. If counting weeks starts then, the time-to-harvest estimates are usually close to accurate.
Having said all that, my wife and I don't count weeks. We just look at the plants and let our intuition guide us. We prefer the mellow high we get from a late harvest. We've never been disappointed by harvesting late.