As far as I know, it will fluctuate up just as much as it does down. I guess the question is how much variance is ok, for a profit increase? If NVC is 2% more profitable than the next coin, but might fluctuate 20% before it gets sold, is that ok?
Hmm, I haven't watched the prices over time. An idea, if it is fluctuating a lot but pretty much stays within two ranges (let's call them MIN and MAX) is to wait until the price is closer to MAX, then sell them off. If the price is closer to MIN, hold on.
I'm not sure how feasible that is with your selling script, though. If the range between MIN and MAX is constantly changing (ex. there are massive swings happening on the coin still), I think that'd be a new thing to evaluate.
And if the MIN->MAX differences are pretty small, just roll as it is because the loss shouldn't be too big.