To everyone in this thread... Remember RideMax is just a tool. They have solid experience behind them but not even Disney knows the answers to some of these questions. Disney uses educated guesses, as does RideMax.
As it is a tool, that does not mean one should shut down their brain (not that your are). If a Sunday, I would use Saturday data, plan Nemo first with an assumed wait time, then make several RideMax itineraries based on different start times. For example, if DL opens at 8AM make a RideMax run (without Nemo) starting the day at 8:30AM, 9AM, 9:30AM and 10AM. Then whenever you finish Nemo use the itinerary that best fits the time you walk off the ride. By this time the mismatch between Saturday and Sunday data and how it affects the rides in Fatasyland will be minimal.
Everyone knows (well, those who pay attention know) that this summer you must ride Nemo first thing in the morning (best option) or last thing at night (for night owls). Even if RideMax had Sunday data it would almost certainly schedule Nemo as the first ride. So work with that.