The most common part of the S-curve by far is the flat bit before and the flat bit after. We just don't graph it because it's boring. Besides which there is no reason at all to assume that this process will follow that shape. Seems like guesswork backed up by hand waving.
Very much handwaving. The question is not meaningful at all without knowing the parameters of the S-curve. It's like saying "I flipped a coin and saw heads. What's the most likely next flip?"
